chemistry revision (copy)

atoms: the basic units of matter that retain the properties of an element.

acids: substances that donate protons (H⁺ ions) in a chemical reaction and have a pH of less than 7.

bases: substances that accept protons and have a pH of greater than 7, often used to neutralize acids.

examples of acids:

• Hydrochloric acid (HCl)

• Sulfuric acid (H₂SO₄)

• Acetic acid (CH₃COOH)

• Nitric acid (HNO₃)

• Citric acid (C₆H₈O₇)

• vinegar

• lemon juice

examples of bases:

• Sodium hydroxide

• Potassium hydroxide

• Calcium carbonate

• baking soda

• soap

• bleach

universal indicator: an indicator of pH levels that changes a substance’s color to determine its pH level, with different colors corresponding to specific pH values ranging from acidic to alkaline, making it a valuable tool in various chemical experiments and applications.

• phenolphthalein: a pH indicator that is colorless in acidic solutions and turns pink in alkaline solutions

• litmus: a substance that is often absorbed into filter paper, turning it red to indicate an acid and turning it blue to indicate an alkali/base

• methyl orange: a ph indicator that turns a substance red when it is acidic and yellow when it’s neutral or alkaline

how to collect hydrogen gas from the reaction between a metal and acid: place diluted hydrochloric acid in a test tube, add a piece of magnesium and then bring a glowing splint to the neck of the test tube so that it goes 'pop' in the presence of the hydrogen gas that is produced

reactions:

• metals and dilute acids: acid + metal → salt + hydrogen

• metal carbonates and dilute acids: acid + carbonate → salt + water + carbon dioxide

neutralisation: acid + base → salt + water

• example: hydrochloric acid reacts with sodium hydroxide

method of preparing crystals from a neutralisation reaction (nickel sulphate):

1. Measure 25 cm³ of dilute sulphuric acid into a 100 cm³ glass beaker. 

2. Add a spatula of nickel(II) carbonate and stir with a glass rod for several minutes. Keep stirring until either all the solid has dissolved or until no more will dissolve.

3. If all of the solid dissolved, add another spatula of nickel(II) carbonate and stir. Keep adding and stirring until no more will dissolve.

4. Use a funnel and filter paper over a conical flask to filter out the excess nickel(II) carbonate.

5. Discard the filter paper. 

6. Pour the filtrate (solution) into an evaporating dish.

7. Place the evaporating dish on a gauze and tripod, and heat over the Bunsen burner. 

8. Boil the filtrate until it is at around half its original volume.

9. Turn off the Bunsen and allow the filtrate to cool. 

10. Leave the evaporating dish to stand on the fume hood overnight. Crystals of pure nickel (II) sulphate will form. These can be filtered out of the solution and allowed to dry on the filter paper.