C3 Flashcards

Question

What is the law of conservation of mass?

Answer 1

Atoms cannot be created or destroyed by chemical reactions. The same atoms are present at the start and end of a reaction. They are just joined in a different way, so the total mass stays the same during the chemical reaction.

Answer 2

You can investigate conservation if mass by carrying out a reaction in a closed system.This is a container in which no substances can enter or escape during the reaction. Examples: -A beaker of reactants in solution where the products are not gases -A flask attached to a gas syringe to stop products in the gas state escaping

Answer 3

C + OO —> OCO

Answer 4

Substances can leave or enter the reaction mixture in a non-enclosed system. This usually happens when a gas is involved as the gas can leave the reaction or join if it is per day airborne.

Answer 5

Aqueous solution

Answer 6

A half equation is a model for the change that happens to one reactant in a chemical equation. Example: 2Na (s) + Cl2 (g) —> 2Nacl (s) Sodium ions form when sodium atoms lose electrons. This equation models the change: Na —> Na^+ + e^- Chloride ions form when chlorine atoms gain electrons. However chlorine atoms are joined together by covalent bonds to make diatomic chlorine molecules, so this is the half equation the models the change: Cl2 + 2e^- —> 2Cl^- Notice you must balance the charges in half equations, not just the number of atoms and the ions they form.

Answer 7

A complete ionic equation shows the ions present in a reaction mixture l. It usually also includes the formulae of any molecular substances present, or substances in their solid state. Example: HCl (aq) + NaOH (aq) —> NaCl (aq) + H2O (l) The ionic equation: H^+(aq) + Cl^- (aq) + Na^+ (aq) + OH^- (aq) —> Na^+ (aq) + Cl^- (aq) + H2O (l) H2O is modelled as H2O as water is a molecular substance (l) Any ions that appear on both sides are spectator II s because they are in the reaction but don’t take part in the reaction. A net ionic equation leaves out the spectator ions. H^+ (aq) + OH^- (aq) —> H2O (l)

Answer 8

The mole is the unit for an amount of substance. One mole of something contains the same number of sheets as the number of carbon atoms. This number is huge. If you could stack a mole of sheets of paper on top of each other, they would reach a quarter size of the way to the centre of our galaxy. It makes little sense to use the mole in everyday life, but it is useful for tiny particles like atoms, molecules l, ions, or electrons.

Answer 9

1 mole is defined as the amount of any substance that contains the same number of entities as there are atoms in 12.0 g of carbon-12 (Mass number 12) Mole is abbreviated to mol in calculations. Eg 1 mol of water contains 1 mol of water molecules. It would also contain 3 mols of atoms because each H2O molecule contains 3 atoms ( 2 hydrogen atoms, 1 oxygen atom.

Answer 10

A The mass of a substance is related to its molar mass and amount by this expression: Mass(g) = molar mass (g/mol) x amount (mol)

Answer 11

One reactant is usually in excess in a reaction mixture. More of it is present than is needed to react with the other reactant, so some is left at the end. The other reactant is in a limiting amount. The amount of product formed determined by the amount of the limiting reactant, not by the one in excess.

Answer 12

The stoichiometry describes the relative amounts of each substance involved, and is to do with these balancing numbers.

Answer 13

mass/molar mass = amount of substance

Answer 14

When the temperature of the mixture increases during a chemical reaction. e.g: -combustion,fuel burning to cook food -neutralisation, for example sodium hydroxide solution reacting with dilute hydrochloric acid

Answer 15

When temperature of a reaction mixture decreases during a chemical reaction. e.g: The reaction between citric acid and sodium hydrogen carbonate in sherbet sweets, which is why they feel cold on your tongue. photosynthesis in plants, which involves carbon dioxide and water reacting to form sugars by using energy in light.

Answer 16

to find if a reaction involving a solution is exothermic or endothermic: 1-Measure the start temperature of a solution in an insulated container 2-Add the other reactant (reacting substance) and stir. 3-Measure the end temperature of the mixture. 4-Calculate the difference between the start temperature and end temperature (wear eye protection and make sure if reacting substances are both liquid they both start at the same temperature)

Answer 17

In a chemical reaction, bonds break in the reactants to produce separate atoms, and then new bonds form between the atoms to make the products. The surroundings and everything except the reacting particles themselves. During a chemical reaction ,energy (usually measured in kilojoules) is transferred: -from the surroundings to break the bonds in the reactants to form separate atoms -to the surroundings from the reacting particles when bonds form between atoms

Answer 18

A reaction profile is a chart that shows the energy involved.

Answer 19

Energy must be transferred to the reactant particles to start most chemical reactions. Activation is the minimum energy required for a reaction to start. It is often provided by a flame or by heating, and it breaks bonds in the reactants.

Answer 20

In endothermic reactions. More chemical energy is stored in the products than in the reactants.

Answer 21

In an exothermic reaction, less energy is transferred to break bonds than is transferred when new bonds form, so the energy change is negative and energy is transferred to the surroundings.

Answer 22

A redox reaction is a reaction in which reduction and oxidation occur at the same time. In terms of oxygen: Reduction = loss of oxygen from a substance Oxidation = gain of oxygen by a substance

Answer 23

A substance will contain oxygen but will then give it to a different substance I.e that substance is the oxidising agent for giving the substance and the other substance is the reduction agent because it causes the other to lose oxygen.

Answer 24

It’s basically the reverse of oxygen Reduction = gain of electrons Oxidation = loss of electrons

Answer 25

An acid is a substance that releases hydrogen ions,h^+ (aq) when it dissolves in water to make an aqueous solution. E.g HCl (aq) —> h^+ (aq) +cl^- Hydrogen chloride gas (HCl) became hydrochloride acid when dissolved in water the solution contains hydrogen ions and chloride ions.

Answer 26

A base is a substance, usually a metal oxide or metal hydroxide that can neutralise acids. If a base can dissolve in water, it is also an alkali.

Answer 27

An alkali releases hydroxide ions, OH^- (aq), when it dissolves in water.

Answer 28

pH < 7 means acidic pH = 7 means neutral pH > 7 means alkaline (0-14), 0 being most acidic, 14 most alkali)

Answer 29

Neutralisation is the reaction between an acid and a base, or an alkali to form a salt and water only. The salt depends on the acid and base used. Acid +base —> salt + water Acid + alkali —> salt + water

Answer 30

The pH changes when neutralisation happens. It increases if a base or an alkali is added to an acid. If enough base or alkali is added to the acid, the pH many increase from less than 7 to more than 7. The opposite happens if an acid is added to a base or alkali. These changes can be gradual or sudden, depending on the reactants.

Answer 31

If you know the base or alkali used, and the acid used, you can predict the salt made. 1-The names of salts have two parts: The first part comes from the base or alkali, the exception being the use of ammonia or ammonium carbonate when the name starts with ammonium. 2- the second part of the name comes from the acid used

Answer 32

H^+ (aq) + OH^- (aq) —> H2O (l) The hydrogen and hydroxide react to make water.

Answer 33

Carbonates are ionic compounds that contain the carbonate ion, CO3^2-

Answer 34

Carbonates react with acids to form a salt, plus water and carbon dioxide In general: Acid + carbonate —> salt + water + carbon dioxide

Answer 35

The salt made depends upon the acid and carbonate used. CaCO3 (s) + 2HCl (aq) —> CaCl2 (aq) + H2O (l) + CO2 (g) The carbon dioxide is released as bubbles in the acid during the reaction. Calcium carbonate is soluble in water but calcium chloride, the salt formed, is soluble in water. This why a lump of calcium carbonate appears to dissolve if you add acid to it.

Answer 36

If a metal reacts with a dilute acid, the reaction produces a salt and hydrogen. In general: Acid + metal —> salt + hydrogen

Answer 37

The salt depends on the acid and metal used. For example, this equation models the reaction between magnesium and dilute hydrochloric acid. Mg (s) + 2HCl (aq) —> MgCl2 (aq) + H2 (g) The hydrogen is released as bubbles in the acid. As the reaction goes on, soluble magnesium chloride forms. This is why a piece of magnesium ribbon appears to dissolve if you put it into acid, even though magnesium itself is insoluble.

Answer 38

A solution consists of a solute dissolved in a solvent. For a given volume of solution, the greater the amount of solute it contains, the greater it’s concentration. For acids: -A dilute acid contains a low ratio of acid to volume of solution -A concentrate acid contains a high ratio of acid to volume solution.

Answer 39

Acids release hydrogen ions, H^+ (aq), in aqueous solution. A covalent bond in the acid molecule breaks, producing a hydrogen ion and a negatively charged ion: Weak acids are partially ionised (only a small fraction of their molecules release H^+ ions) Strong acids are fully ionised (all of their molecules release H^+ ions)

Answer 40

CH3COOH(aq) <=>CH3COO^- (aq) + H^+ (aq) The symbol <=> shows that reaction does not go to completion

Answer 41

HNO3 (aq) —> H^+ (aq) + NO3^- (aq)

Answer 42

I’m aqueous solution, as the concentration of H^+ (aq) ions increases by a factor of 10, the pH of a solution decreases by 1) An acid has a lower pH (it’s solution is more acidic) when it is concentrated than when it is dilute. A strong acid has a lower pH than a weak acid at the same concentration.

Answer 43

Electrolysis is a process in which an electric current is passed through a compound, causing a chemical change.

Answer 44

You need 3 components -an electrolyte -two electrodes -an electrical supply such as a power pack or battery.

Answer 45

The negative electrode, the cathode And The positive electrode, the anode.

Answer 46

Positive ions gain electrons at the cathode and become atoms Negative ions lose electrons at the anode and become atoms

Answer 47

Anions = negative ions Cations = positive ions

Answer 48

A binary ionic compound is a compound that contains just two elements.

Answer 49

Molten lead bromide, PbBr2(I), consists of lead ions and bromide ions. You can model what happens at the electrodes using half equations: Lead is produced at the cathode: Pb^2+ + 2e^- —> Pb Bromine is produced at the anode: 2Br^- —> Br2 + 2e^-

Answer 50

You say that the ions have been discharged.

Answer 51

Overall, ions move to an oppositely charged electrode during electrolysis. The concentration of ions close to each electrode goes down as ions gain or lose electrons to become atoms. Other ions in the electrolyte can move to replace them by diffusion and convection. This could not happen in ionic compounds in the solid state, which is why ionic compounds in the solid state cannot conduct electricity.

Answer 52

Inert electrodes are not changed during electrolysis l. They’re usually made from unreactive metals such as copper or platinum l, or from graphite. Inert electrodes can be used for the electrolysis of many ionic compounds in their liquid state or in aqueous solution (dissolved in water)

Answer 53

Water is naturally partially ionised. It contains small concentrations of hydrogen and hydroxide ions. H2O(l) <=> H^+ (aq) + OH^-(aq)

Answer 54

During electrolysis hydrogen ions are discharged at the cathode as hydrogen in its gas state, and hydroxide ions are discharge at the anode, forming water and oxygen in its gas state. 4H^+(aq) + 4e^- —> 2H2 (g) (reduction) 4OH^- (aq) —> 2H2O(l) + O2 (g) + 4e-(oxidation)

Answer 55

An aqueous solution contains ions from a dissolved ionic compound. Unlike a molten electrolyte, it also contains hydrogen ions and hydroxide ions from water. The reactions of each ion compete at the electrodes and only one ion is discharged at each electrode: -hydrogen is produced at the cathode, but if ions from a less reactive metal then hydrogen are present, that metal is produced instead. -Oxygen is produced at the anode, but if ions from an element in group 7 element are present at high enough concentration then the group 7 element is produced.

Answer 56

You look at a reactivity series

Answer 57

(most reactive) Potassium Sodium Calcium Magnesium Aluminium Zinc Iron Tub Lead (Hydrogen) Copper Silver Gold Platinum (Least reactive)

Answer 58

Cu^2+, H^+

Answer 59

Cu^2+, H^+

Answer 60

SO4^2-, OH^-

Answer 61

SO4^2-,OH^-

Answer 62

Electroplating is a type of electrolysis that uses non-inert electrodes; these electrodes change during electrolysis.

Answer 63

-The cathode is the object you want to coat -The anode is a piece of the metal you want to coat the object with -The electrolyte is a solution containing ions of the coating metal. Eg: A solid silver piece of jewellery would be expensive, so electroplating is often used to coat copper or nickel jewellery with silver: -The cathode is the piece of jewellery -The anode Is the piece of silver -The electrolyte is silver nitrate solution Silver nitrate solution is used because it contains silver ions and all nitrate salts are soluble in water, so you know the silver nitrate will dissolve.

Answer 64

During electroplating, metal ions from the electrolyte are discharged on the surface of the object (the cathode). These ions are replaced by metal ions leaving the surface of the anode. Overall, metal leaves the anode and is deposited on the object. This process continues until the anode is used up.

Answer 65

Silver atoms lose electrons at the anode: Ag —> Ag^+(aq) + e^- Silver ions gain electrons at the cathode: Ag^+(aq) + e^- —> Ag^+ (s)

Answer 66

-The conducting part of electrical cables is made from copper. However, copper obtained straight from copper ores must be purified so it can conduct electricity well enough to be useful. -Copper is purified in a similar way to electroplating, except that both electrodes are made from copper. The anode is impure copper and the cathode is very pure copper -Copper(II) sulfate solution is commonly used as the electrolyte. -During electrolysis, the cathode gains copper atoms and increases in mass, while the anode loses copper atoms and decreases in mass. Impurities from the anode fall off and collect underneath it.

Answer 67

Progress of the reaction (time)