20 experiments found
Clear filtersAn acid and an alkali neutralise each other to form a salt and water; at the end point the pH is 7
Add dilute sodium hydroxide drop by drop to dilute hydrochloric acid with an indicator, watch the pH change, and find the exact point of neutralisation.
Air is a mixture: about 78% nitrogen, 21% oxygen, 1% argon and a little carbon dioxide
Trap air in a tube with damp iron wool over water, watch the water rise as the iron rusts, and compare fresh air with breathed-out air.
One mole of a substance is 6.022 × 10²³ particles (Avogadro's number), and its mass in grams equals the molar mass; so moles = mass ÷ molar mass, and particles = moles × 6.022 × 10²³
Atoms and molecules are far too small to count one by one, so chemists count them in moles. Put water, carbon, salt, carbon dioxide or glucose on a balance, change the mass, and find the moles and the number of particles.
Pure carbon exists in different forms called allotropes: crystalline ones (diamond, graphite, fullerene, graphene) have their atoms in a regular pattern, amorphous ones (coal, charcoal, coke, lampblack) do not; carbon compounds such as methane and sugar contain other elements too
Test twelve substances, from diamond and graphite to charcoal, soot and sugar, for hardness, electricity and what they are made of. Sort them into crystalline carbon, amorphous carbon and carbon compounds.
In a chemical reaction atoms are only rearranged, never made or destroyed, so the total mass stays the same (the law of conservation of mass); mass only seems lost when a gas escapes from an open container
Weigh a flask of vinegar with baking soda before and after they react, once with the flask open and once closed with a balloon. Find out whether mass is really lost.
Atoms are not created or destroyed in a reaction, so a balanced equation has the same number of each kind of atom on both sides
Change the numbers in front of each substance until every kind of atom is the same on both sides of the equation, watching the molecules as you go.
Higher temperature and smaller pieces make reactions faster
Drop fizzy tablets into cold, room-temperature and warm water, and crush one. Time which reaction finishes first.
Physical properties such as solubility, miscibility, melting and conductivity can be used to identify and group substances
Test common laboratory substances with water, heat and a conductivity tester, and group them by how they behave.
A solution's particles are smaller than 1 nm and let light through unseen; a colloid's (1 to 1000 nm) scatter a beam of light (the Tyndall effect) but pass through filter paper; a suspension's are bigger, settle and are filtered out
Shine a torch through twelve mixtures, from salt water and vinegar to milk, fog and muddy water, filter them, and sort them by the size of their particles.
The concentration of a solution by mass is mass of solute ÷ mass of solution × 100, where the solution is the solute plus the solvent; more solute or less water makes it stronger
Dissolve sugar in water to make sharbat. Change the grams of sugar and water, find the mass per cent, and see that different amounts can make solutions of the same strength.
Metals can be arranged in order of reactivity; a more reactive metal displaces a less reactive one
Put magnesium, zinc, iron and copper in dilute acid and compare the fizzing, then see which metals can push copper and zinc out of their salt solutions.
Metals above hydrogen in the reactivity series react with dilute acids to give hydrogen: Zn + 2HCl → ZnCl₂ + H₂; the amount of gas is set by whichever reactant runs out first, and hydrogen burns with a squeaky pop
Drop zinc, magnesium, iron or copper into dilute hydrochloric acid and collect the gas over water. Change the amounts and find out which runs out first, then test the gas with a burning splint.
The number of protons decides the element; electrons fill shells 2, 8, 8; ions have unequal protons and electrons; isotopes have different numbers of neutrons
Add protons, neutrons and electrons to build atoms of the first 20 elements, arrange the electrons in shells, and make ions and isotopes.
Every atom is made of protons and neutrons in a tiny nucleus with electrons around it; the number of protons decides which element it is
Add protons, neutrons and electrons one by one and see the atom you make: its name, its mass and how its electrons sit in shells. Then turn carbon into nitrogen with a single proton.
NaHCO₃ + CH₃COOH → CH₃COONa + H₂O + CO₂: one mole (84 g) of baking soda gives one mole (44 g, about 24 L) of carbon dioxide and needs one mole (60 g) of acetic acid
Drop 2 to 20 g of baking soda into vinegar and blow up a balloon with the carbon dioxide. Use the equation and moles to find the mass and volume of the gas and how much vinegar the soda needs.
Solubility is the most of a substance that dissolves in 100 g of water at a given temperature; sugar's solubility rises steeply with temperature, but salt's hardly changes
Stir sugar or salt into water at different temperatures until no more dissolves. See how hot water dissolves far more sugar, while salt hardly changes, and why syrup for sweets is made hot.
Food spoils when microbes grow in it; microbes need water, warmth and time, so food keeps longer when we take the water out, keep it cold, heat it to kill the germs, or pickle it in acid or oil
Look at twelve kitchen foods, from sun-dried fish to mango achar, find out how long each keeps and what stops the microbes, and sort them by the way they are preserved: drying, cold, heat or pickling.
Dissolving salt makes water denser; an object floats when the liquid is denser than the object, so an egg floats once the salty water is denser than the egg
Drop an egg into a glass of water and stir in salt, a spoonful at a time, until the egg floats. Then try an old egg, which floats in plain water, and find out why cooks use this to test eggs.
Water boils when its vapour pushes as hard as the air above it; higher up the air pressure is lower, so water boils at a lower temperature (about 1 °C lower for every 300 m) and food cooks more slowly
Boil a pot of water at the seaside, in Kathmandu, Shimla, Leh and at Everest base camp. See how the boiling point falls as you climb, and why dal takes so much longer to cook up high.
Each fuel gives a fixed heat per gram, its calorific value, but a stove passes only part of it to the pot; grams burnt = heat needed ÷ (calorific value × efficiency), so a good fuel in a good stove burns far less
Boil 1, 2 or 5 litres of water on an LPG stove, a kerosene stove, a coal stove, an open wood fire or a dung-cake chulo. See the heat the water needs and how many grams of each fuel burn to give it.