# Moles and reactions

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• Created by: racheon
• Created on: 02-03-14 14:42
Define stoichometry.
The molar relationship between the relative quantities of substances taking part in a reaction.
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What does a balanced equation tell you when talking about quantities?
The reacting quantities that are needed to prepare a required quantity of a product and the quantities of product formed by reacting together known quantities of reactants.
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Sodium and chlorine react to form sodium chloride: 2Na(s)+Cl₂(g)->2NaCl(s). Calculate the masses of Na and Cl₂ that would form 2.925g of NaCl [Ar: Na-23, Cl-35.5].
1. n=m÷M=2.925÷23+35.5=2.925÷58.5=0.05mol. 2. Na-2 mol so 0.05 mol, Cl₂-1 mol so 0.025 mol, NaCl-2 mol so 0.05 mol. 3. Na: m=nxM: 0.05x23=1.15g. Cl₂: 0.025x71=1.775g.
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Heated 2.55g of sodium nitrate decomposes: 2NaNO₃(s)->2NaNO₂(s)+O₂(g). Work out the amount of gas produced in dm³. [Ar: Na-23, N-14, O-16].
1. n=m÷M=2.55÷23+14+(16x3)=2.55÷85=0.03mol. 2. NaNO₃-2 mol so 0.03 mol, O₂-1 mol so 0.015 mol. 3. V=nx24=0.015x24=0.36dm³.
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0.23g of sodium reacts with water to form 250cm³ of aqueous sodium hydroxide: 2Na(s)+2H₂O(l)->2NaOH(aq)+H₂(g). Work out how much gas is produced in cm³ and the concentration of sodium hydroxide produced. [Ar: Na-23, H-1, O-16]
1. n=m÷M=0.23÷23=0.01. 2. Na-2 mol so 0.01 mol, H₂-1 mol so 0.005 mol. V=nx24 000=0.005x24 000=120cm³. 3. NaOH- 2 mol so 0.01 mol. c(NaOH)=nx1 000÷V=0.01x1 000÷250=0.04 mol dm³.
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What are the 3 ways to work out moles?
From mass: n=m÷M. From gas volumes: n=V(in dm³)÷24 or n=V(in cm³)÷24 000. From solutions: n=cxV(in dm³) or n=cx(V[in cm³]÷1 000).
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## Other cards in this set

### Card 2

#### Front

What does a balanced equation tell you when talking about quantities?

#### Back

The reacting quantities that are needed to prepare a required quantity of a product and the quantities of product formed by reacting together known quantities of reactants.

### Card 3

#### Front

Sodium and chlorine react to form sodium chloride: 2Na(s)+Cl₂(g)->2NaCl(s). Calculate the masses of Na and Cl₂ that would form 2.925g of NaCl [Ar: Na-23, Cl-35.5].

### Card 4

#### Front

Heated 2.55g of sodium nitrate decomposes: 2NaNO₃(s)->2NaNO₂(s)+O₂(g). Work out the amount of gas produced in dm³. [Ar: Na-23, N-14, O-16].

### Card 5

#### Front

0.23g of sodium reacts with water to form 250cm³ of aqueous sodium hydroxide: 2Na(s)+2H₂O(l)->2NaOH(aq)+H₂(g). Work out how much gas is produced in cm³ and the concentration of sodium hydroxide produced. [Ar: Na-23, H-1, O-16]

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