C8- Acids And Alkalis

Question 1

How are hazards of acids or alkalis shown

Answer 1

By international symbols - they indicate the precautions needed to be taken when handling them

Question 2

How is the acidity or alkalinity of a solution measured

Answer 2

With a ph scale of 0 - 14 7 = neutral

Indicators can be used - that change colour

Universal indicator is made from a mixture of different indicators

Question 3

Tell me about the indicator litmus

Answer 3

Blue in alkaline solution

Red is acid

Question 4

Tell about methyl orange indicator

Answer 4

Yellow in alkali

Red in acid

Question 5

Tell me about the indicator phenolphthalein

Answer 5

Pink in alkali

Colourless in acid

Question 6

What happens when an atom loses electrons

Answer 6

Positive ion is formed

Question 7

What are polyatomic ions

Answer 7

Former when small groups of atoms held by covalent bonds lose or gain electrons - eg OH

Question 8

When happens to ions in acids

Answer 8

They produce an excess of hydrogen ions (H+) when they dissolve in water

Question 9

What happens to ions in alkalis

Answer 9

Alkalis produce exceed hydroxide ions in water

Question 10

How does concentration change

Answer 10

The higher the number of hydrogen ions in a certain volume, the higher a concentration

Same with alkalis with hydroxide ions

Neutral solutions - eg pure water have low and equal concentrations of hydrogen ions and hydroxide ions

Question 11

What are bases

Answer 11

Substances that neutralise acids to form a salt and water only

All metal oxides are based

Question 12

What happens in neutralisation

Answer 12

Hydrogen ions in the acid combine with oxide ions to form water

This removes hydrogen ions and so the ph increases to become neutral

The salts are produced by replacing the hydrogen ions with metal ions

Question 13

Why is an excess of base always added

Answer 13

To make sure that all the acid is used up

Question 14

How do you make sure the prepared salt is pure

Answer 14

The mixture is filtered to remove the residue (unreactive metal oxide) from the filtrate, leaving only the salt and water

Question 15

How do crystallisation of the salt occur

Answer 15

Allowing the water to evaporate - leaving crystals

Question 16

What’s a base that can dissolve in water

Answer 16

A soluble base is called an alkali wooow

Ph values above 7

Question 17

Tell me about group 1 hydroxides - alkali bases

Answer 17

Eg NaOH - balance out

But group 2 tend to be like Ca(OH)_2 as more hydroxide needed to produce a neutral complex

Question 18

What happens to temperature when the neutralisation reaction

Answer 18

The mixture becomes warmer

Question 19

What’s a balanced equations

Answer 19

The number of atoms of each element must be the same on both sides

Question 20

What happens if you try get some soluble salts from alkalis with the solution NOT being neutral

Answer 20

Otherwise you will contaminate the salt with an excess of one reactant

Question 21

How can you obtain a neutral solution with only water and salt

Answer 21

Titration

Question 22

What happens in a titration

Answer 22

Acid is added from a burette to a fixed volume of alkali in a conical flask

Use a measuring cylinder to measure out the alkali but a pipete is more accurate for repeatable measurements

A few drops of indicator are added to the alkali so you can follow the reaction

The end point is when the indicator changes colour

Methyl orange or phenolphthalein are used Becuase their obvious colour changes give you a sharp end point

Question 23

What’s a burette

Answer 23

A tall peice of glassware with 0.1cm^3 graduations

Question 24

Tell me the steps to make a pure dry salt

Answer 24

Carry out a titration

Note the exact volume of acid neutralise the alkali

Use the burette to add the correct volume of acid without the indicator

Evaporate the water from the solution formed