Formulae, Equations & Hazards Flashcards

All 18 cards in this deck

Give the formulae of the molecules of hydrogen, oxygen, nitrogen and chlorine as they exist as elements.

$H_2$, $O_2$, $N_2$, $Cl_2$ — these elements are diatomic.

When are brackets used in a chemical formula?

e.g. a compound of $Ca^{2+}$ and $OH^-$

When more than one of an ion containing several atoms is needed: $Ca(OH)_2$

True or false? Writing chlorine as CL instead of Cl is still acceptable in a formula.

False. Only the first letter of a symbol is a capital, so it must be $Cl$ (and $Cl_2$ for the molecule).

What are the steps to write a word equation for a described reaction?

e.g. calcium hydroxide reacting with hydrochloric acid

1. Names of reactants on the left, joined by +: calcium hydroxide + hydrochloric acid
2. Arrow →
3. Names of products on the right: → calcium chloride + water

What are the steps to write a balanced symbol equation from a word equation?

e.g. magnesium + hydrochloric acid → magnesium chloride + hydrogen

1. Write the correct formulae: $Mg + HCl \rightarrow MgCl_2 + H_2$
2. Count each type of atom on both sides
3. Add numbers in front of formulae until they match: $Mg + 2HCl \rightarrow MgCl_2 + H_2$

What do the state symbols (s), (l), (g) and (aq) mean?

solid, liquid, gas, aqueous (dissolved in water)

True or false? An equation can be balanced by changing the small subscript numbers inside a formula.

False. Only the large numbers in front of formulae may be changed; changing subscripts changes the substance.

What is a spectator ion?

An ion that is present but unchanged on both sides of the equation, so it is left out of the ionic equation.

What are the steps to write an ionic equation from a full balanced equation?

e.g. $MgO(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2O(l)$

1. Write dissolved ionic substances as separate ions
2. Cancel the spectator ions ($Cl^-$)
3. Write what is left, balanced: $MgO + 2H^+ \rightarrow Mg^{2+} + H_2O$

What is the ionic equation for the neutralisation of an acid by an alkali?

$H^+(aq) + OH^-(aq) \rightarrow H_2O(l)$

True or false? In a balanced ionic equation the total charge must be the same on both sides.

True. Both the atoms and the total charge must balance.

Give the two purposes of hazard symbols on containers.

To indicate the dangers associated with the contents, and to inform people about safe-working precautions in the laboratory.

What does the 'oxidising' hazard symbol tell you about a substance, e.g. potassium manganate(VII)?

It provides oxygen, so other substances burn more fiercely.

What precaution should be taken when preparing chlorine gas in the laboratory, and why?

Use a fume cupboard, because chlorine is a toxic (poisonous) gas.

What precaution should be taken when using concentrated hydrochloric acid, and why?

Wear gloves and goggles/safety glasses, because concentrated hydrochloric acid is corrosive (burns skin and eyes).

What does the 'corrosive' hazard symbol tell you about a substance?

It eats away at whatever it comes into contact with and can cause serious burns to the skin and eyes.

e.g. concentrated sodium hydroxide solution

What does the '(highly) flammable' hazard symbol tell you about a substance, and what precaution follows?

It ignites easily, so keep it away from naked flames and sparks, such as a lit Bunsen burner.

e.g. ethanol

What is the difference between a hazard and a risk?

A hazard is the thing that is able to do harm, e.g. a flammable liquid. The risk is the likelihood that harm actually happens, e.g. lower if the liquid is kept away from flames.