Foundations in Chemistry: Acids, Bonding Redox

What is an acid?

substances that release H+ ions when dissolved in water. Proton donors

What is a strong acid?

an acid that fully dissociates when dissolved in water

Give 3 examples of strong acids

HCl, H2SO4, HNO3

Give an example of a weak acid

CH3COOH, ethanoic acid

What is the difference between a base and an alkali?

an alkali is a base that dissolves in water, releasing OH- ions

How can you identify a salt in a reaction?

It will be an ionic compound (metal and non-metal).

What are the products of a reaction between an acid and a metal carbonate?

salt, water and carbon dioxide

What are the common bases?

metal oxides, metal hydroxides, metal carbonates and alkalis

Give the ionic equation of a neutralisation reaction

H+ + OH- = H2O

What are titrations used for?

Finding out exactly how much acid is needed to neutralise a quantity of alkali

Give an example of an indicator used in a titration

methyl orange, phenolphthalein

What is a standard solution?

a solution of known concentration

Describe the preparation of a standard solution

1) Work out mass of substance needed to be weighed by multiplying the concentration by the volume to get the mole. Then, multiply the mole by the molar mass to get the mass.

2) Dissolve substance in a beaker with distilled water. Then, pour solution into a volumetric flask, including the rinsings from the beaker. Add distilled water until bottom of meniscus is on the graduation line

What is a meniscus?

The curved upper surface of a liquid in a tube

Describe how to carry out an acid-base titration

1) Add 25cm^3 of the solution of known concentration into a conical flask

2) Place flask on white tile and add indicator (e.g. methyl orange)

3) Add solution of unknown concentration and volume into a burette

4) Turn on tap, swirling the flask until there is a colour change signalling the end-point

5) Calculate the volume of solution added. Repeat titration until there are at least 2 concordant results

What is the process to calculate unknown concentration?

1) Write a balanced equation for the reaction

2) Calculate the amount in moles of the known solution that reacted

3) Use stoichiometry to calculate the amount in moles of the unknown solution that reacted

4) Calculate the unknown concentration by dividing the moles by the volume

How can the percentage uncertainty be calculated?

((uncertainty number of readings) / measured value ) 100

Define oxidation number

a number assigned to an element in chemical combination which represents the number of electrons lost or gained by an atom of that element in the compound

What is the rule for assigning an oxidation number to a pure element?

the oxidation number is zero

What is the rule for assigning an oxidation number to monatomic ions?

the oxidation number is equal to ionic charge

What does the sum of the oxidation numbers equal?

the overall charge of the compound (e.g. in a polyatomic ion, it equals the overall charge on the ion)

What is a redox reaction?

a chemical reaction involving both oxidation and reduction

What is oxidation?

the loss of electrons and increase in oxidation number

What is reduction?

the gain of electrons and decrease in oxidation number

Definition of an Acid

releases H+ ions

definition of an alkali

releases OH- ions

What is a base?

a substance that can accept H+ ions

A sample of magnesium contained 24Mg: 78.60%; 25 Mg: 10.11%; 26Mg: 11.29%.

Calculate the relative atomic mass of this sample of Mg.

Give your answer to four significant figures.

[2 marks]

2.

The mass spectrum of a sample of tellurium is shown in Figure 1.

Use Figure 1 to calculate the relative atomic mass of this sample of tellurium.

Give your answer to one decimal place.

A sample of rubidium was analysed in a mass spectrometer to produce the mass spectrum below.

(i)

Use this mass spectrum to help you complete the table below.

(ii)

Calculate the relative atomic mass of this rubidium sample. Give your answer to three significant figures.

m

Antimony is found naturally in a number of minerals including stibnite. Stibnite typically contains 5% of Sb2S3. Antimony can be obtained by reducing Sb2S3 with scrap iron.

(1)

(i)

Sb_S3 + 3Fe → 2Sb + 3FeS

How many moles of Sb2S3 are in 500 kg of a typical sample of stibnite containing 5% by mass of Sb2S3

molar mass of Sb2S3 = 340 g mol-1'; relative atomic mass of Sb = 122

Calculate the mass of antimony that could be obtained by processing 500 kg of stibnite.

Nickel makes up 25% of the total mass of a fifty pence coin. A fifty pence coin has mass of 8.0 g.

(i)

Calculate how many moles of nickel atoms are in a fifty pence coin.

what is a strong acid?

acid that completely dissociates in solution

what is a weak acid?

something that only partially dissociates in solution

What is an ion?

charged atom or molecule

Definition of an Isotope?

atoms of the same element with the same number of protons and elections but a different number of neutrons

What is an Ionic Bond?

electrostatic attraction between positive and negative ions

What is a covalent bond?

a bond formed between two or more atoms due to electrostatic attraction from a shared pair of electrons

What elements can form hydrogen bonds?

Nitrogen (N), Oxygen (O) and Fluorine (F)

How many electrons are in a P-subshell?

6

How many electrons can a s-subshell hold?

2

How many electrons can a d-subshell hold?

10

How many bonding pairs are in a linear bond? Name an example. What is the bond angle?

2 bonding pairs, Beryillium Chloride or Carbon Dioxide.

How many bonding pairs and lone pairs are in a non-linear molecule?

2 bonding pairs and 2 lone pairs

Bond angle of NON-linear molecules? And an example

104.5, H2O

Pyrimidal molecules: How many lone pairs, bonding regions, angle and an example?

1 Lone pairs

3 bonding regions

107 degree angle

Ammonia NH3

Trigonal Planar: how many bonding regions, lone pairs and what is the bond angle?

3 Bonding regions/pairs

No lone pairs

120 degrees

BF3 is an example

Octahedral molecules: How many bonding pairs?

6

What is the bond angle of an Octahedral molecule?

90 degrees

What is the bond angle in a tetrahedral molecule?

109.5 degrees

How many bonding regions does a tetrahedral molecule have?

4

Barium metal can be extracted from barium oxide, BaO, by reduction with aluminium. 6BaO + 2A/ 3Ba + Ba3Al2O6

Calculate the mass of barium metal that could be produced from reduction of 500 g of barium oxide using this method.

Nickel makes up 25% of the total mass of a fifty pence coin. A fifty pence coin has mass of 8.0 g.

(i) Calculate how many moles of nickel atoms are in a fifty pence coin.

Aqueous silver nitrate can be used as a test for halide ions. A student decided to carry out this test on a solution of magnesium chloride. The bottle of magnesium chloride that the student used showed the formula MgCl2.6H20.

The student dissolved a small amount of MgCl2.6H20 in water and added aqueous silver nitrate to the aqueous solution.

(i) What is the molar mass of MgC/2.6H20?

In gmol-1

What is produced when an acid reacts with a metal?

Salt + Hydrogen gas is produced.

What is made when a Oxide reacts with an acid?

Salt and water is produced.

What is made when a metal hydroxide reacts with an acid?

Salt and water is produced.

What is made when a carbonate reacts with an acid?

Salt, water and carbon dioxide is produced.

What is made when a hydrogen carbonate reacts with an acid?

Salt, water and carbon dioxide is produced.

What is made when an acid reacts with ammonia?

ONLY an ammonium salt is made.