4 Acids and Redox

Question 1

Whay do all acids have in common?

Answer 1

All acids contain hydrogen (release H+ ions).

Question 2

Define a strong acid.

Answer 2

A strong acid releases all its hydrogen atoms into

solution as H+ ions and completely dissociates

in aqueous solution.

Question 3

Define a weak acid.

Answer 3

A weak acid only releases a small proportion of its available hydrogens into solution as H+ ions.

A weak acid partially dissociates in aqueous solution.

Question 4

What links metal oxides, metal hydroxides, metal carbonates, and ammonia?

Answer 4

They are all bases.

Question 5

What is an alkali?

Answer 5

An alkali is a base that dissolves in water relasing hydroxide ions.

Question 6

Acid + Alkali → ?

Answer 6

Acid + Alkali → Salt + Water

Question 7

Write an equation for CuO reacting

with hydrochloric acid.

Answer 7

CuO_(s) + 2HCl_(aq) → CuCl_2(aq) + H₂O_(l)

Question 8

State the formula for ammonium ethanoate.

Answer 8

CH₃COONH₄

Question 9

What is the formula for calcium nitrate?

Answer 9

Ca(NO₃)₂

Question 10

What is the formula for sodium sulfate?

Answer 10

Na₂SO₄

Question 11

Acid + metal oxide/hydroxide → ?

Answer 11

salt + water

Question 12

Write an equation for magnesium carbonate

reacting with dilute hydrochloric acid.

Answer 12

MgCO₃ + 2HCl_(aq) → MgCl_2(aq) + H₂O_(l) + CO_2(g)

Question 13

Use equations to explain why sulfuric acid is sometimes described as a strong acid and a weak acid together?

Answer 13

Strong acid fully dissociates to release one H+ ion:

H₂SO_4(aq) → H+_(aq) + HSO₄^-_(aq)

Weak acid partially dissociates to release some H+ ions:

HSO₄^-_(aq) → H+_(aq) + SO₄^2-_(aq)

Question 14

What is a standard solution?

Answer 14

A standard solution is a solution of known concentration.

Question 15

Describe the technique for making a standard solution.

Answer 15

1. Weigh solid.
2. Dissolve solid in beaker.
3. Transfer solution to volumetric flask then rinse beaker several times and add it to the flask.
4. Fill flask carefully until the bottom of the meniscus lines up exactly with the graduation line.
5. Invert the flask to mix solution.

Question 16

Why is the last digit recorded in a titration

always a 0 or a 5?

Answer 16

Each burette reading is measured to +/- 0.05cm³

The uncertainty is in the last digit.

Question 17

When do you know you have done enough titration trials to stop?

Answer 17

You stop doing trials once you have two accurate titres that are concordant - agreeing to withing 0.10cm³.

Question 18

The indicator changes colour at the ____________ of the titration.

Answer 18

endpoint

Question 19

The oxidation number is always ___________ for elements in their natural state.

Answer 19

Zero.

Question 20

What is the oxidation number of oxygen in H₂O₂?

What is the usual/most common oxidation number for oxygen in compounds?

Answer 20

In peroxide (H₂O₂), oxygen is -1.

Oxygen is most commonly -2.

Question 21

What is the oxidation number of oxygen in F₂O?

Answer 21

Oxygen is +2 in this compound.

This is because fluorine is the most electronegative element and takes to -1 charge every time.

Question 22

What is the oxidation state of hydrogen in CaH₂?

Answer 22

Hydrogen is -1 in CaH₂.

Hydrogen usually has +1 oxidation state in compounds,

but when it is a hydride it is -1.

Question 23

What is the oxidation number of sulfur in sulfuric acid?

Answer 23

H₂SO₄ Oxidation number of sufur is +6.

Question 24

What is the formula for a nitrate ion?

Answer 24

Nitrate: NO₃^-

Question 25

What is the formula for a nitrite ion?

Answer 25

Nitrite: NO₂^-

Question 26

Most commonly:

Oxidation is the __________ of oxygen.

Reduction is the ____________ of oxygen.

Answer 26

Most commonly:

Oxidation is the addition of oxygen.

Reduction is the removal of oxygen.

Question 27

Define reduction.

Answer 27

Reduction is the gain of electrons.

Question 28

Define oxidation.

Answer 28

Oxidation is the loss of electrons.

Question 29

Reduction is a(n) ______________ in oxidation number.

Oxidation is a(n) ______________ in oxidation number

Answer 29

Reduction is a decrease in oxidation number.

Oxidation is an increase in oxidation number.

Question 30

True/False

In a balanced full equation, if one species is oxidised, something else must be reduced.

Answer 30

True