Formulae, Equations & Hazards Flashcards

All 19 cards in this deck

What are the formulae of the diatomic elements hydrogen, oxygen, nitrogen and chlorine?

$H_2$, $O_2$, $N_2$ and $Cl_2$ — they exist as molecules of two atoms.

What is the formula of methane?

$CH_4$ — one carbon atom joined to four hydrogen atoms.

What is the formula, including the charge, of the sulfate ion?

$SO_4^{2-}$

Complete the general word equation: metal + acid → ?

salt + hydrogen
e.g. sodium + hydrochloric acid → sodium chloride + hydrogen

Complete the general word equation: metal carbonate + acid → ?

salt + carbon dioxide + water

What are the steps to turn a word equation into a balanced symbol equation?
e.g. hydrogen + chlorine → hydrogen chloride

1. Write the correct formulae: $H_2 + Cl_2 \rightarrow HCl$
2. Count the atoms of each element on both sides: 2 H and 2 Cl on the left, 1 H and 1 Cl on the right
3. Put big numbers in front of formulae until they match: $H_2 + Cl_2 \rightarrow 2HCl$

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

(s) solid, (l) liquid, (g) gas, (aq) aqueous — dissolved in water.

True or false? To balance an equation you may change the small subscript numbers inside a formula.

False. Only the big numbers in front of formulae may be changed; changing a subscript changes the substance.

What does the hazard symbol showing a flame mean?

Flammable — the substance catches fire easily.

What does the hazard symbol showing a skull and crossbones mean?

Toxic — the substance can cause death if swallowed, breathed in or absorbed through the skin.

What does the hazard symbol showing liquid dripping onto a hand and a surface, burning them, mean?

Corrosive — the substance attacks and destroys skin, eyes and other materials.

State a safe-working precaution for using a substance labelled corrosive.

Wear eye protection (and gloves) and avoid skin contact.

What precaution should be taken in a practical that produces a toxic gas?

Carry out the reaction in a fume cupboard.

What is the difference between a hazard and a risk?

A hazard is anything that could cause harm. The risk is the chance that someone is actually harmed by that hazard.

What does the hazard symbol showing a flame above a circle mean?

Oxidising — the substance gives out oxygen, which makes other substances burn more strongly. Store and use it away from flammable materials.

What does the hazard symbol showing an exclamation mark mean?

Harmful / irritant — the substance can irritate the skin, making it red or causing blisters.

What is the formula, including the charge, of the hydroxide ion?

$\mathrm{OH^-}$

Write the formula of the carbonate ion, showing its charge.

$\mathrm{CO_3^{2-}}$: one carbon atom and three oxygen atoms with an overall 2− charge.

Salts called nitrates all contain the same negative ion. What is its formula?

$\mathrm{NO_3^-}$, the nitrate ion (charge 1−).