Women in Science: Valentina Tereshkova, First Woman in Space

Image Credit: NASA

Most people know that 1961 Yuri Gargarin was the first man in space. Most people also know that 1969 Neil Armstrong was the first man on the moon. However, few people know when the first woman went to space.

The first woman in space was Valentina Tereshkova in 1963 – only two years after Gargarin’s tour. This is an incredibly short time considering how long it took the Americans to send their first woman to space. Sally Ride launched with the space shuttle Challenger in June 1983 – 22 years after the first American, Alan Shepard, went to space.

Having left education early, Valentina worked at a textile factory in a small village in Russia. Many might consider this early career unlikely for a future cosmonaut. However, Valentina was a passionate parachutist. This hobby later qualified her to join the cosmonaut training program. Recruitng parachutists to the space program was not uncommon at the time because early cosmonauts and astronauts had to parachute out of their space craft when landing back on Earth.

After winning the race of putting the first man into space, Soviet leadership was determined to also win the race of launching the first woman. Therefore, they sent out incognito spotters to parachuting clubs to find women suited for the cosmonaut training program.

After further tests, Valentina was selected for training along with four other women. Three of them had university degrees in technology and engineering. So, why was Valentina chosen before them? Soviet leader Nikita Khrushchev got the final pick and he chose Valentina mainly because she was the best fit for party propaganda. Her father had died as a soldier during World War II and she was clearly of the working class.

Valentina launched into space aboard Vostok 6 on 16 June 1963 and orbited the Earth 48 times. After three days she landed in the Altay region in Kazakhstan.

After her return, Valentina was greatly celebrated by the Soviet leadership and became an important propaganda figure. However, she never flew in space again.

Author’s Comment

Despite being chosen as the first woman in space partly for propaganda reasons, I believe, we can learn something important from Valentina Tereshkova’s career.

Valentina left school early and worked in a textile factory, but managed to join the astronaut program. She pulled off a major career change. This means it is never too late to learn something new, change your career or apply for that training program or course you always wanted to do.

Teenagers today are often told that they need to figure out exactly what they want to do with their lives by the ages of 15 or 16. After that that’s it. You are stuck with your choice. Valentina’s story shows that this is not true. You can start out as a textile worker and end up going to space.

Reading Exercise: The History of the Atomic Model

Democritus’ atoms

Around 440 BC, Greek philosopher Democritus was the first to suggest the existence of atoms, tiny particles that make up all matter. The word atom comes from the Greek ”atomos” meaning indivisible.

However, most of his colleagues, especially Aristotle, did not agree with Democritus. Instead, they thought that matter was made up of the four ”elements” fire, water, wind and earth.

Dalton’s spheres

It took over 2000 years until another scientist would challenge Aristotle’s ”element” theory.

In 1803, John Dalton, an English teacher from Manchester, carried out experiments proving that all matter is made up of tiny particles. He chose to use Democritus’ name and called them atoms.

In Dalton’s model atoms were tiny, hard spheres that vary in size and mass, but cannot be split into smaller pieces.

Thomson’s plum pudding

It took a much shorter time to reach the next step in the discovery of the atomic model.

J.J. Thomson, another English scientist, discovered the electron in 1897 and developed the plum pudding model of the atom for which he received the Nobel prize in 1906.

The plum pudding model said that the tiny negative electrons were distributed in a positive mass inside the atom. The electrons were like negative raising in a positive plum pudding dough.

Rutherford’s gold foil experiment

The next experiment to develop the atomic model even further were carried out by one of Thomson’s former students, Ernest Rutherford, who was originally from New Zealand.

In 1909, Rutherford and his team conducted one of the most important experiments in the history of science. They used a gold foil which was bombarded with alpha particles (= Helium nuclei which have 2 protons and 2 neutrons).

If Thomson’s plum pudding model were true, you would expect all alpha particles to punch holes through the positive ”dough” and pass straight through the foil.

The results looked somewhat different. Most alpha particles did pass straight through the gold foil. However, some particles did not pass through and bounced back. This suggested that there were parts in the foil where mass was very concentrated, while the rest seemed to be empty space.

As a consequence, Rutherford introduced the modern planetary model of the atom where the electrons circulate around a nucleus. The nucleus is small, but contains most of the atom’s mass and is where the alpha particles bounced back in his experiment. The major part of the atom is empty space where the alpha particles could pass through.

By the way, Ernest Rutherford received a Nobel prize as well. However, it was for discovering the concept of half-life for radioactive substances rather than his work on the atomic model.

Tasks:

  1. Draw a timeline including the four stages of the atomic model’s development.
  2. Describe what the word ”atom” means.
  3. Describe what atoms were like in Dalton’s atomic model.
  4. State what Thomson discovered.
  5. Describe what atoms were like in Thomson’s atomic model.
  6. Describe the gold foil experiment Rutherford conducted.
  7. Explain how the gold foil experiment showed that Thomson’s theory was wrong.
  8. Describe what atoms are like in Rutherford’s model.
  9. Challenge: Find out how the atomic model developed further. You could look at the work of Niels Bohr, Werner Heisenberg and James Chadwick.

Iron Man’s Suit, Thor’s Hammer and Captain America’s Shield. – What are they made of?

Image credit: Shutterstock, 6 May 2019.

Iron Man’s Suit

You could say that Tony Stark was a bit under pressure when he developed his first Iron Man Suit, captured by terrorists and having suffered an injury by a shrapnel that is moving dangerously close to his heart. With the help of a fellow captive Stark builds a generator to power an electromagnet keeping the shrapnel from killin him as well as the very first Iron Man Suit that he uses to escape.

While this prototype suit was welded together from steel, and was therefore actually made from iron, Stark kept improving and developing his armours over time for different applications. This means that the Iron Suit materials changed over time.

Stark must have quickly replaced steel with a different material since it is a very heavy and rusts easily. The following armours were probably made from titanium since it is much lighter than steel, but still extremely strong. In addition to its strength, this metal can resist extreme temperature changes as well as chemicals such as acids, alkalis and water.

Stark might have chosen the alloy “nitinol” later on when improving his armours. This alloy is a mixture of the metals titanium and nickel. Therefore, it has all the above mentioned advantages of titanium, but it also has two special features called “shape memory” and “super elasticity”. These two properties help the alloy to return to its original shape after deformation. This means the material can “self-heal”, a huge advantage when fighting super villains like Thanos and Ultron.

For his final suits Stark seems to have moved away from metals completely. At the beginning of “Avengers: Infinity War”, he proudly tells Dr Strange that his new suit is made from carbon nanofibers. These fibers are very long and thin threads of carbon. Woven together, carbon nanofibers are both stronger and lighter than titanium and nitinol. This sounds like the perfect material for an Iron Man Suit (which is actually not made from iron as we have seen).

Thor’s Hammer and Axe

(Mjolnir and Stormbreaker)

Thor’s Hammer, Mjolnir, was forged from the heat of a neutron star, called Nidavellir. These incredibly heavy, dense stars are made when giant stars die in supernovas and their cores collapse. Due to the heat and pressure protons and electrons inside the core melt together to form neutrons. There are no repulsive forces between the neutrons, which means they pack together extremely tightly creating a relatively small, but super heavy object, the neutron star.

Unfortunately, all of this does not exactly tell us which material Thor’s Hammer and Axe are made from. I personally always assumed that it was in fact made from the neutrons inside the star. This would explain why it is so incredibly heavy.

However, in “Avengers: Infinity War”, this does not seem to be the case. Thor, Rocket and Groot travel to Nidavellir to forge a new weapon for Thor. In the scene that shows the forging of Stormbreaker, Thor’s Axe, it is clear that the heat to melt the metal comes from the neutron star. But that does not seem to be the case for the metal inside the boiler.

So, what else could Mjolnir and Stormbreaker be made from? Thor’s Hammer is always said to be extremely heavy. This means it must be at least partially made from a very dense metal. The two densest metals on today’s periodic table are osmium and iridium. These two materials could be a part of Mjolnir’s and Stormbreaker’s composition.

Besides being heavy, Thor’s weapons should also be reasonably strong when fighting Thanos, Ultron and other intergalactic villains. However, osmium and iridium are not very strong metals. Therefore, the material for Thor’s weapons would have to be an alloy (a mixture of metals) between osmium and/or iridium as well as a stronger metal like steel (which already is an alloy itself). With a mixture like this, you might just get the right material for Thor’s Hammer and Axe.

Captain America’s Shield and Black Panther’s Suit

Captain America’s Shield and Black Panther’s suit are both made from vibranium, a very rare metal that does not naturally exist on Earth. The only source of vibranium is the African kingdom Wakanda, the home of Black Panther. The country has a prehistoric meteorite to thank for this incredible natural resource. Vibranium fuelled Wakanda’s rapid technological development making it one of the most advanced nations on Earth.

In the movy “Captain America: The First Avenger” we get some demonstrations about what makes vibranium so special. Moreover, Howard Stark claims that vibranium is stronger than steel, which is proven later in the movie when Captain America’s shield defends projectiles from machine guns and even withstands rocket grenades.

In addition to being extremely strong, vibranium also has a low density, which means that it is very light. Howard Stark also reveals that the name vibranium comes from the fact that the material absorbs any kind of vibrations including sound.

There have been some discussions regarding the nature of vibranium. Some say it could be an alloy or a composite material since no pure metal on Earth comes close to its extraordinary properties. However, all composite materials and alloys that we know of have to be made in longer processes by humans, they do not exist naturally. Therefore, it is very unlikely, in my opinion, that such materials have reached Wakanda on a meteorite.

In my personal view, the meteorite must have either contained vibranium in its uncombined form or bound up in an ore. Ores are rocks that contain enough of a metal to extract it, so the Wakandans could have found an easy way to extract the vibranium. However, both these two scenarios would mean that vibranium is a new, unknown element.

Nevertheless, everyone is entitled to their own view on the Marvel Universe.

Sources

M. Lorch and Andy Miah: ”The Secret Science of Superheroes”, Royal Society of Chemistry, 2017, Chapter 7 and 8.

Nitinol: https://www.memry.com/intro-to-nitinol, 6 May 2019.

Carbon nanofibers: http://www.materialsforengineering.co.uk/engineering-materials-features/top-14-materials-for-2014/58395/, 6 May 2019.

Neutron star: http://astronomy.swin.edu.au/cosmos/N/Neutron+Star, 6 May 2019.

Movie: Captain America: The First Avenger, 2011.

Movie: Thor, 2011.

Movie: Iron Man, 2008.

Movie: Captain America: Civil War, 2016.

Movie: Black Panther, 2018.

Movie: Avengers: Infinity War, 2018.

Our connectedness to nature and what Christmas lights have to do with it

Image credit: M. Ehlers, pexels.com.

It has become a tradition for my fiancé and me to take a walk looking at the Christmas lights when we are at his family’s home in Derbyshire, England. This year it struck me that instead of Santas, angels, bells and stars, we saw a lot of lights showing scenes derived from nature.

There were glowing plastic deer and trees in almost every garden. Many had invested in projectors. This latest Christmas light fashion projects moving pictures of falling snowflakes onto your house, giving the impression of real snow falling. Other gardens had huge, inflatable polar bears and penguins.

I found these Christmas light choices interesting, because they seemed like an unconscious try to reconnect with nature. Right now, our Western societies are getting increasingly disconnected from nature. This means we spend less time outdoors, interact less with animals as well as plants and feel less like being part of nature.

Although, it is difficult to put numbers on our connectedness to nature, the RSPB (Royal Society for the Protection of Birds) published a study in 2013 after interviewing children aged eight to twelve. The young participants had to agree or disagree with 16 statements such as “being outdoors makes me happy” and “humans are part of the natural world”.

The report showed that four in five children in the UK are disconnected from nature. This means children spend less time playing outdoors and interacting with nature. Consequently, today’s youngsters feel less empathy for animals and plants, less responsibility for the environment and less like being part of nature.

I assume you can already guess where this is going? Exactly, disconnecting from nature is thought to result in people caring less about the extinction of species, pollution and global warming. To value something and safeguard it, you need to be engaged with it. But if we disconnect from nature, we will not care about its fate any longer.

So, disconnecting from nature is obviously bad for nature. But will it affect us humans? The answer is it does seem to affect our health. Research has linked visits to parks and other green spaces in cities to better mental and physical health. Some of the health benefits are obvious. If you spend a lot of your time in parks, you are more physically active. Nevertheless, a lot of research still needs to be done on this subject to find all the links. The main message is: We humans also profit from a good connectedness with nature.

Back to our Christmas light story. As a society we are disconnecting from nature. Still people choose a lot of nature scenery for their Christmas lights which shows that people still value nature in a way. The Christmas lights I saw felt like they romanticised animals and plants like a memory from better days a long time ago.

This is where I want to remind people, that nature is still here. Yes, we are losing many species and ecosystems, but all is not lost yet!

Deer still roam across a great number forests and meadows in the Northern hemisphere and the last time I checked we still had trees too. If we decide to protect and safeguard our local ecosystems, there is no need to buy plastic copies of its animals and plants. We could experience real animals and plants for free. The RSPB has a few tips for those wanting to protect their local wildlife and ecosystems.

If we decide to effectively fight climate change with real, lasting changes to our lifestyles and economies, there is no need to project falling snowflakes onto our houses. We could have real snowfall for free. The campaign Sustainability for All has some very good suggestions on how to fight climate change with simple lifestyle choices.

So, what can you do to reconnect and stay connected to nature?

Indoors, buy and grow plants in your house, apartment, balcony or garden. Watch nature documentaries. Read books about animals and plants. Feed birds in your garden or on your balcony.

Outdoors, go to the local park for a walk or a run, look for plants and animals you don’t know and google them or look them up elsewhere. Take your kids, encourage them to play in the mud and look for plants as well as insects. Go to the zoo. Go to the country side for a walk, a run or a bike ride. Go to the local beach or lake for a swim in the summer instead of the indoor swimming pool.

There are countless possibilities. Find the ones you enjoy most.

But whatever you do, do not get glowing plastic deer and trees for your garden!

Active reading exercise: How do muscles work?

Image: D. Keeno, 17 November 2017.

How do muscles work?

Muscles work by getting shorter. We say that they contract.

Muscles are attached to bones by strong tendons. When a muscle contracts, it pulls on the bone, and the bone can move if it is part of a joint.

Muscles can only pull, but not push. This would be a problem if a joint was controlled by just one muscle. As soon as the muscle had contracted and pulled on a bone, that would be it, with no way to move the bone back again. The problem is solved by having muscles in pairs, called antagonistic pairs.

To move the bone back the second muscle of the antagonistic pair contracts. Examples of antagonistic pairs are biceps and triceps.

How does your forearm move?

The elbow joint lets our forearm move up or down. It is controlled by two muscles, the biceps on the front of the upper arm, and the triceps on the back of the upper arm.

The biceps and the triceps are an antagonistic pair.

  • When the biceps muscle contracts, the forearm moves up.
  • When the triceps muscle contracts, the forearm moves down. 

    This solves the problem. To lift the forearm, the biceps contracts and the triceps relaxes. To lower the forearm again, the triceps contracts and the biceps relaxes.

Tasks:

1. Box how muscles work.

2. Circle what attaches muscles to bones.

3. Underline what happens when muscles contract.

4. Underline why muscles need to work in antagonistic pairs.

5. Describe in your own words how antagonistic pairs work.

6. Explain in your own words how your forearm moves.

Reading exercise: Antibiotics and bacteria resistance

The following text is written for pupils with low reading ages to help them study the topic of antibiotics and bacteria resistance.

Before antibiotics

Think back to the last time you cut yourself. Can you imagine that cut becoming infected with bacteria – so seriously infected that you would die?

Before the discovery of antibiotics, there was nothing anybody could do. Bacteria could kill 80 percent of people with infected wounds.

Who would have thought a mouldy plate would lead to this?

In 1928, Alexander Fleming, a doctor at London’s St. Mary’s Hospital, found that a mould on a discarded plate had antibacterial properties. This mould was ‘penicillin’. Penicillin is an antibiotic.

Antibiotics kill bacteria and slow down their growth. A bacterium consists of one single cell and antibiotics disturb their cell functions. Antibiotics do not work against viruses because a virus consists of a DNA fragment instead of a cell.

Human life expectancy increased rapidly by eight years when antibiotics were first introduced in the 1930s.

Bacteria resistance

Within four years of penicillin being introduced onto the market, bacteria resistance was being reported. Bacteria resistance means that an antibiotic no longer kills the bacteria.

Today bacteria resistance against commonly used antibiotics is increasing rapidly around the world and a growing problem.

Active Reading Exercise: What is an echo?

The following active reading exercise includes a short test and tasks suitable for students aged 11 to 14 when studying waves and sound.

When waves hit a surface, they are reflected. This means they bounce off the surface and come back. For example, light is reflected by the surface of a mirror.

When you are high up in the mountains and call out in a loud voice. Your sound waves will be reflected by a mountain surface nearby and you can hear it coming back after a few seconds. This is called an echo.

You can measure the distance from where you stand to the mountain surface and time how long it takes until your hear the echo. With this information you can calculate the speed of sound.

This principle is used by animals like dolphins and bats for navigation. They send out sound waves and listen for their echo. This helps them to work out how far away predators or food are. When used like this echoes are called sonar.

Sonar is also used by submarines for navigation. Submarines send our sound waves and listen for the echo to know their own position. They can also detect other submarines and ships.

Tasks:

  1. Box the words in the text you do not know.
  2. Highlight what happens to waves when they hit a surface.
  3. Highlight the word that describes the reflection of sound waves.
  4. Circle the two types of waves that are mentioned in the text.
  5. a) Underline the animals that use sonar.
  6. b) Underline how submarines use sonar.

*Extension: Explain what a dolphin needs to know to work out the distance to a fish when using sonar.

Which liquid dissolves candy canes fastest?

  1. Get four beakers. Fill one beaker with cold water, one with hot water, one with oil and one with vinegar. The hot water can be taken from the kettle.
  2. You need to put one candy cane in each beaker at the same time and start your timer.
  3. Record your observations.
  4. Record the time when the first candy cane has dissolved. BUT, do not stop the timer.
  5. Record the time when the 2nd and 3rd candy cane have dissolved too.
  6. Write your conclusion and state which liquid dissolves the candy cane fastest and which is the slowest.

Orange peel flamethrower

Here you can see the orange peel flamethrower in action.

The instructions are the following:

All you need is a candle and some orange peel. First, you have to light the candle. Then fold your orange peel, the shiny, orange side should face the candle. As you squeeze the peel, oils from the peel will squirt into the flame. The oils ignite and produce beautiful sparks in the candle flame. In addition, this experiment smells very nice and Christmassy.

So, go a head and surprise your family and friends with some amazing chemistry at Christmas dinner.

Of Poinsettia and Gingerbread – Christmas Chemistry Experiments

Title image credit: Maurice Snook, ACS (2011).

Why not try some Christmas chemistry with your science and chemistry students during the last week before Christmas? The easy-to-do Christmas experiments in this article can be used to shake things up a little just before you break up for turkey roast and minced pie. With the instructions come suggestions about what previous knowledge can be discussed together with these experiments.

1 Orange Peel Flamethrower

This experiment is very easy and can be done by the students or as a demonstration. It is suitable for ages 11 to 16. It can even be done with or demonstrated to primary children if you trust them with candles.

All you need is a candle and some orange peel. First, you have to light the candle. Then fold your orange peel, the shiny, orange side should face the candle. As you squeeze the peel, oils from the peel will squirt into the flame. The oils ignite and produce beautiful sparks in the candle flame. In addition, this experiment smells very nice and Christmassy.

This short practical or demonstration can be used to discuss the flammability of different organic substances. The oil burning in the flames is a fat, which can be used to recap carbon chemistry. The combustion of the oil can be linked to oxidation reactions and exothermic/endothermic reactions.

2 Poinsettia pH Paper and Indicator

2.1 Background

This experiment is suitable for ages 11 to 18. It is adapted from a procedure by A.M. Helmenstine (2017).

The poinsettia flower originates form warmer climates. Nevertheless, many people use them as a decoration in their house during the winter holidays. Their red leaves contain substances that change colour when they are in contact with an acid or a base. For this reason, poinsettias are one of the natural pH indicators such as turmeric and red cabbage.

2.2 Procedure

You will need a poinsettia flower, a beaker, water, scissors, filter paper, a bunsen burner or a heating plate, a tripod, a funnel, a pH meter or universal indicator paper, 0.1 M HCl (hydrochloric acid), vinegar (dilute acetic acid), baking soda solution (10 g/ 1 dm3)  0.1 M NaOH (sodium hydroxide) and any other acids or bases you would like your pupils to test.

With scissors cut a few petals of a poinsettia plant into very small pieces and put them into a beaker. Add just enough water to cover the petal pieces and boil with Bunsen flame or heating plate for a few minutes until the water has taken the colour of the petals. Then, filter the liquid with a funnel and filter paper into a conical flask. This solution can already be used as a pH indicator solution.

To make pH paper, some of the solution needs to be poured onto a petri dish. Afterwards, pH paper is placed onto the petri dish to soak in the indicator solution. The filter paper has to dry and can finally be cut into pH strips.

The pH paper and indicator solution can be tested against different acids and bases, such as 0.1 M HCl (hydrochloric acid), vinegar (dilute acetic acid), baking soda solution (10 g/ 1 dm3) and 0.1 M NaOH (sodium hydroxide).

Poinsettia-1024x679

2.3 pH Chart Challenge and Links to Previous Knowledge

The exact colour range for pH values can vary for different poinsettia plants. Students can be challenged to make their own poinsettia pH chart. For this, they will have to measure the pH of the test solutions above with a pH meter or universal indicator paper which already has a colour chart. They can then match their poinsettia indicator colour to the pH meter or universal indicator chart.

Obviously, you can link this practical to indicators and natural indicators as well as everything the pupils already know about acids and bases.

3 Thermal Decomposition of Sodium Bicarbonate and its Importance for Gingerbread

3.1 Background

This experiment is suitable for ages 14 to 18. A-level and more able KS4 students could even be challenged to plan their own investigation and experiment to answer the question. The question is: What happens to sodium bicarbonate when it is heated in the oven during the baking process?

Sodium bicarbonate (NaHCO3) is an important part of many gingerbread and cookie recipes. Sodium carbonate is also the major ingredient in baking powder which is often used instead of sodium bicarbonate. The task of sodium bicarbonate is to release gases when heated. These gases form bubbles and are trap

ped inside the dough during the baking process. This is important since the gas raises the cake and provides the “fluffiness” in cakes and cookies.

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This experiment can be adapted and shortened by omitting the calculations and deciding which reaction equation is right. This would still demonstrate that sodium bicarbonate loses mass when heated during baking as it releases water and carbon dioxide. The importance of this for baking can still be discussed and stressed with students.

3.2 Procedure

Pupils are provided with three possible reaction about what could happen during the reaction and they have to find out what is happening:

  1. NaHCO3 -> CO2 + NaOH
  2. 2 NaHCO3 -> H2O + 2 CO2 + Na2O
  3. 2 NaHCO3 -> H2O + CO2 + Na2CO3

For the experiment, pupils need to weigh in and write down an exact amount of sodium bicarbonate. 2 to 3 g are suitable. The scales should be as exact as possible for this task. The sodium bicarbonate is put into a crucible. NOTE: It is important that the students write down the weight of the empty crucible as they will have to weigh the thermal decomposition product inside the crucible. They should also mark their crucible with their name.

The crucible should be heated for 15 to 20 minutes at 180 degrees Celsius. This can be done in any oven. (Maybe your food department can help you out, if you do not have any oven and the crucibles have been thoroughly cleaned before the experiment.) It is also possible to heat the crucible over a bunsen flame for about 20 minutes.

More able pupils and A-level students can be asked to decide themselves at which temperature and for how long they want to heat their sample. (Having been told about the use of sodium bicarbonate in baking powder, they should be able to tell that a normal baking temperature and time for cookies should be sufficient.)

After heating the sample, students need to weight it again and write down the new mass.

3.3 Calculations

This part can be omitted. If you do, you should provide your pupils with the information about chemical reaction directly and discuss the importance of it for baking.

Their task now is to figure out which reaction is taking place during the thermal decomposition of sodium bicarbonate. They need to be given the information that the gasses formed are carbon dioxide (CO2) and water (H2O).

A-level and more able KS4 students can try to have a go at these calculations themselves. In other classes, I would do the calculation together with the class. Or at least model one of the three possible calculations,

The reaction actually happening is the third one from the list above:

2 NaHCO3 -> H2O + CO2 + Na2CO3

Molar masses (M):  NaHCO3: 84 g/mol;  H2O: 18 g/mol;  CO2: 44g/mol;   Na2CO3: 106 g/mol

Key equations:  substance amount = mass/molar mass     n = m/M

mass = substance amount x molar mass    m = n x M

The mass of sodium bicarbonate before the experiment is sodium bicarbonate NaHCO3, let us assume it was 2.0 g. This means we had 0.024 mol of sodium bicarbonate in the beginning (n = 2/84). For two mole of sodium bicarbonate, one mole of sodium carbonate, Na2CO3, is formed. This means we have 0.012 mol sodium carbonate which equals 1.272 g (m = 0.012 x 106).

Does this mass, 1.272 g, match the mass that we have after the experiment?

You can do the calculation also for sodium hydroxide (NaOH; M = 40 g/mol) and sodium oxide (Na2O; M = 62 g/mol) to show that it must be sodium carbonate which is formed. The calculated masses for sodium hydroxide and sodium oxide will not match the mass from the experiment after heating!

For sodium hydroxide, we would have a mass of 0.48 g (m = 0.012 x 40) and for sodium oxide 1.488 g (m = 0.024 x 62), if 2.0 g (= 0.024 mol) sodium bicarbonate are weighed in before the experiment.

3.4 Gingerbread and Links to Previous Knowledge

This experiment can be used to discuss thermal decompositions and endothermic reactions. As seen with the calculations, conversions between mas and amount of substance can be practiced and revised. In addition, the conversion of mass can be discussed.

My experience is that pupils really like the link to everyday life which is baking, especially during Christmas time. This aspect should really be stressed when doing this experiment.

When teaching this experiment earlier, I provided my students with gingerbread recipes when they left after the session. The students really appreciated this little give-away and I can recommend if you want to do this experiment.

4 Silver Christmas Decorations with Tollen’s Reagent

4.1 Background

This experiment is most for A-level students if they are to conduct it themselves. For younger ages, it is better as a demonstration. It is essentially Tollen’s test and demonstrates how reducing sugars reduce silver ions to silver. The method is adapted from the Royal Society of Chemistry and the Nuffield Foundation (2015).

4.2 Procedure

You will need bottles that should be as small as possible. (Small booze bottles are useful.)  These bottles need to be cleaned thoroughly and rinsed with purified water before the experiment. Further, 25 cm3 beakers, funnels, pipettes, silver nitrate (AgNO3, s), potassium hydroxide (KOH, s), glucose (dextrose) (= reducing sugar), ammonia solution, (NH3, aq) and concentrated nitric(V) acid, (HNO3, aq) and purified water are needed.

The following solutions need to be prepared, but NOT mixed before the experiment. The solutions should suffice for about 10 experiments.

  1. 5 g of silver nitrate in 500 cm3 of purified water to make a 0.1 M solution
  2. dissolve 11.2 g of potassium hydroxide in 250 cm3 of purified water to make a 0.8 M solution
  3. dissolve 2.2 g of glucose in 50 cm3 of purified water.

The following instructions are for a 50-cm3-bottle, the amounts will have to be adjusted for larger or smaller bottles. Place 15 cm3 of the silver nitrate solution in a 25-cm3-beaker. In a fume hood, add a few drops of ammonia until the brown precipitate dissolves. The colourless complex ion, [Ag(NH3)2]+ is formed.

Now, pour 7.5 cm3 of the potassium hydroxide solution into the 25-cm3- beaker and a dark brown precipitate of silver(I) oxide (Ag2O) is formed. Then, add a few more drops ammonia solution till the precipitate dissolves again.

The formed clear solution is called Tollen’s reagent. Pour this solution into your small bottle using a funnel and add 1 ml of the glucose solution with a pipette. Screw the cap on the flask and swirl the solution so that the whole of the inner surface of the flask is wetted. The solution will turn brown. Continue swirling until a silver mirror forms after 2 minutes.

4.3 Christmas Tree Decoration and Links to Previous Knowledge

After the experiment, wash the solution down the sink with plenty of water. Rinse out the flask well with water. A string can be added around the neck of the flask, so it can be hung up in a Christmas tree at home.

Obviously, this experiment can be used to link to learning about reducing sugars, but also to redox reactions. It can even be used to discuss noble metals and why silver is easily reduced considering the electrochemical series.

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References

  1. Poinsettia pH Paper and Indicator: M. Helmenstine (2017), https://www.thoughtco.com/poinsettia-ph-paper-604229, (25 November 2017)
  2. Silver Christmas Decorations with Tollen’s Reagent: Royal Society of Chemistry and the Nuffield Foundation (2015), Learn Chemistry, http://www.rsc.org/learn-chemistry/resource/res00000822/a-giant-silver-mirror-experiment?cmpid=CMP00004158 (25 November 2017).
  3. Images: com (25 November 2017)