Chemical Changes

Question 1

Which ions make aqueous solutions acidic

Answer 1

Hydrogen ions (H+)

Question 2

Which ions make aqueous solutions alkaline

Answer 2

Hydroxide ions (OH-)

Question 3

What is the pH scale

Answer 3

Ranges from 0 - 14 to measure a solutions acidity or alkalinity

Question 4

pH ranges for acid, alkali and neutral

Answer 4

Acid - less than pH 7 (1 is strongest)

Neutral - pH 7

Alkali - Greater than pH 7 (14 is the strongest)

Question 5

What can be used to measure pH

Answer 5

Universal indicator

pH probe

Question 6

What colour is phenolphthalein in acid and alkali

Answer 6

Acid - colourless

Alkali - pink

Question 7

What colour is methyl orange in an acid and alkali

Answer 7

Acid - Red

Alkali - Yellow

Question 8

What colour is blue litmus paper in an acid and alkali

Answer 8

Acid - turns red

Alkali - STAYS blue

Question 9

What colour is red litmus paper in an acid and alkali

Answer 9

Acid - stays red

Alkali - turns blue

Question 10

Problem with using universal indicator to text pH

Answer 10

Colours can be misinterpreted

Doesn’t provide an exact pH value

Question 11

What can be said about the concentration of H+ ions in an acid with a pH of 1

Answer 11

There is a high concentration of H+ ions, making it a strong acid

The lower the pH of the acid, the higher the concentration

Question 12

What can be said about the concentration of OH- ions in an alkali with a pH of 8.5

Answer 12

There is a low concentration of OH- ions, making it a weak alkali

The lower the pH of the alkali the lower the concentration of OH- ions

Question 13

If pH decreases by one unit, what happens to the concentration of hydrogen ions

Answer 13

Increases by a factor of ten (x10 each time)

Question 14

What is neutralization reaction

Answer 14

A reaction between acid and a base

Question 15

What happens in an acid-alkali neutralisation reaction

Answer 15

H+ ion from the acid react with the OH- ions from the alkali to form water

Question 16

What is the ionic equation for a neutralisation reaction

Answer 16

H+ (aq) + OH- (aq) ——> H2O (I)

Question 17

What does the term concentrated and dilute mean when talking about acid

Answer 17

Concentrated acids have more moles of acid per unit volume of water than dilute acids

The concentration of an acid is not the same as strength. Strength refers to whether the acid has complete dissociates in water or not

Question 18

What can be said about the strength of an acid that only partially dissociates in water

Answer 18

Weak acid

Question 19

What is a base

Answer 19

Any substance that reacts with an acid to form salt and water only

Question 20

Are alkali soluble or insoluble bases

Answer 20

Soluble bases

Question 21

What are the products when an acid reacts with a metal

Answer 21

Salt and hydrogen

Acid + metal —-> salt + hydrogen

Question 22

What are the products when an acid reacts with a metal oxide

Answer 22

Salt and water

Acid + metal oxide —-> salt + water

Question 23

What are the products when an acid reacts with a metal hydroxide

Answer 23

Salt and water

Acid + metal hydroxide —-> salt + water

Question 24

What are the products when an acid reacts with a metal carbonate

Answer 24

Salt, water and carbon dioxide

Acid + metal carbonate —-> salt + water + carbon dioxide

Question 25

Why are metal oxides normally bases rather than alkalis

Answer 25

Metal oxides are normally insoluble. Alkalis are soluble

Question 26

Describe chemical test for hydrogen

Answer 26

Insert a lit splint into a test tube of gas A squeaky pop will be heard if hydrogen is present

Question 27

Describe chemical test for carbon dioxide

Answer 27

Bubble the gas through limewater (calcium hydroxide) Limewater turns cloudy if carbon dioxide is present

Question 28

When a soluble salt is prepared from an acid and an insoluble reactant, why is excess of the the insoluble reactant added in

Answer 28

To ensure all the acid reacts

Question 29

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