6.1 Acids & Bases

Question 1

What is an acid?

Answer 1

Any substance that forms an aqueous solution with a pH less than 7

Question 2

What is an alkali?

Answer 2

A base that dissolves in water and produces hydroxide ions to form a solution with a pH greater than 7

Question 3

What does the salt that forms from an acid and an alkali contain?

Answer 3

The anion from the acid and the cation from the alkali

Question 4

What can you use to work out the concentration of an acid or an alkali?

Answer 4

Neutralisation reactions

Question 5

How would you use a neutralisation reaction to work out “Make 250cm of a 31.4g/dm of sodium hydroxide” (7)

Answer 5

• First work out how many grams of solute you need using the formula: mass = concentration x volume. Here, its 31.4 g/dm x 0.250 = 7.85.
• Now weigh out this mass - put an empty weighting container on a mass balance and reset it to zero, then add the correct mass.
• Add the solid to a beaker containing about 100 cm of deionised water and stir until all the solute has dissolved. Use some deionised water to wash the weighing container and pour the washings into the beaker - this makes sure all of the solid is transferred.
• Tip the solution into a volumetric flask of the right size. Use a funnel to make sure it all goes in.
• Rinse the beaker and stirring rod with deionising water and add that to the flask too. This makes sure there’s no solute clinging to the beaker or rod.
• Top the flask up to the correct volume (250) with more deionised water. Make sure the bottom of the meniscus is on the line. When you get close to the line, use a dropping pipette to add the last bit of water one drop at a time.
• Stopper the flask and turn it upside down a few times to mix the solution.

Question 6

What is universal indicator?

Answer 6

It gives a wide range of colours, ranging from deep red (acid) to deep purple (alkali)

Question 7

Describe how a pH meter can be used

Answer 7

You can measure the pH of a solution by using a pH probe that is connected to a pH meter. By dipping the probe into a solution, you can electronically measure the pH and get a numerical reading on the meter.

Question 8

What will a reaction with an acid and a base always produce?

Answer 8

A salt and a water

Question 9

What examples of three acids?

Answer 9

• Hydrochloric acid
• Sulfuric acid
• Nitric acid

Question 10

What are two examples of bases?

Answer 10

• Sodium hydroxide
• Calcium carbonate

Question 11

What are two reasons why using a pH probe is more reliable than using an indicator?

Answer 11

• Determining the colour of an indicator is subjective
• A probe produces a more accurate result