1 Moles 2 Flashcards
A solution of HCl is 1 M
What does the M stand for?
M stands for Molar
M = mole / dm3
Rearrange the concentration equation in terms of moles
n = C V
What volume does 0.5 moles of chlorine gas occupy?
12 dm3
V = n x molar volume = 0.5 mole x 24dm3/mol = 12dm3
1 mole of any gas occupies 24dm3
50 cm3 of NaOH was added to the acid.
What is this volume in dm3?
1000 cm3 = 1 dm3
50 cm3 / 1000 = 0.050 dm3
Why must we use a burette when titrating?
It allows us to measure any amount of acid/alkali with a small uncertainty. We can also add drop by drop near the end point (neutralisation point)
This burette - if used properly - measures to +- 0.1 cm3
How many moles are there in 24 dm3 of carbon dioxide gas?
1 mole of carbon dioxide molecules
1 mole of any gas occupies 24dm3 at room temp
During titration, why must we use a pipette to measure out the solution into the conical flask?
Using a pipette decreases the uncertainty in our volume reading
If this pipette is used properly it measures to +- 0.03 cm3 !!
What colour is methyl orange in acid and alkali?
red in acid
yellow in alkali
What is the relationshipe between moles, mass and RFM
moles = mass/ RFM
Define concentration
Concentration is moles per unit volume of a solution
Why must you swirl your conical flask during titration?
To fully mix the acid and alkali - ensure that the reaction is complete.
Does using a pipette and burette which both measure volume to a high resolution improve the accuracy or reliability of your results?
Using a pipette and burette and reading these at eye level and to the bottom of the meniscus improves the accuracy of your results.
Read the burette below
42.30 cm3
Do not forget to add the zero - you can tell if it is exactly on the 0.30 or if it is 0.35!!
What do we call the process of filling a burette on the floor using a funnel?
This is called ‘charging’ the burette
What colour is litmus in alkali?
blue
2H2 + O2 ⇒ 2H2O
What volume of oxygen is needed to fully react with 30 dm3 of hydrogen?
2H2 + 1O2 ⇒ 2H2O
15dm3 of oxygen
1 mole of any gas occupies the same volume- therefore use the short cut!
Mole ratio of H2 : O2 is 2 : 1
What are concordant results?
Concordant results are when the volume of solution added are within 0.2 cm3 of each other.
Any concordant results are then averaged.
What colour is litmus in acid?
red
25.00 cm3 of sodium hydroxide was added to a conical flask. 10.0 cm3 of 2M hydrochloric acid was needed to neutralise the sodium hydroxide.
Calculate the moles of HCl used.
n = CV
n = 2M x 0.010 dm3 =0.02 mol
20.00 cm3 of sodium hydroxide was added to a conical flask. 10.0 cm3 of 2M hydrochloric acid was needed to neutralise the sodium hydroxide.
n = CV
n = 2M x 0.010 dm3 =0.02 mol of acid was used
HCl : NaOH is a 1:1 mole ratio
Therefore 0.02 mol of NaOH reacted
Calculate the concentration of NaOH?
C = n/V
C = 0.02 / 0.020 = 1 mol/dm3 OR 1M
Name the equipment below
A- volumetric flask
B- pipette
C- burette
What steps do you follow when calculating the concentration of an acid needed to neutralise a known concentration of alkali?
- Use n = CV to find moles of alkali
- Use mole ratio between acid and alkali from balanced equation
- used C = n/V to find concentration of acid
DO NOT FORGET - VOLUME MUST BE IN dm3
What volume does 1 moles of ammonia gas occupy?
24 dm3
V = n x molar volume = 1 mol x 24dm3/mol= 24dm3
1 mole of any gas occupies 24dm3
2H2 + O2 ⇒ 2H2O
What volume of hydrogen is needed to fully react with 20 dm3 of oxygen?
2H2 + 1O2 ⇒ 2H2O
40dm3 of hydrogen
1 mole of any gas occupies the same volume- therefore use the short cut!
Mole ratio of O2 : H2 is 1 : 2
How many moles are there in 48dm3 of oxygen gas?
2 moles of oxygen molecules
n = V / molar volume = 48 dm3 / 24dm3/mol = 2 mol
1 mole of any gas occupies 24dm3 at room temp
Rearrange the concentration equation in term of volume
V = n / C
How can a 2M solution of sulfuric acid be used to make a 0.2M solution of sulfuric acid?
Pipette 10 cm3 of 2M sulfuric acid and place it into a 100cm3 volumetric flask.
Fill the volumetric flask with distilled water so that the bottom of the meniscus is at the marked line on the neck of the flask.
What volume does 2 moles of argon gas occupy?
48 dm3
V = n x molar volume = 2 mol x 24dm3/mol = 48dm3
1 mole of any gas occupies 24dm3
What colour is phenolphthalein in alkali?
pink
2H2 + O2 ⇒ 2H2O
What volume of water vapour is produced from 70 dm3 of hydrogen?
2H2 + O2 ⇒ 2H2O
70dm3 of water vapour
1 mole of any gas occupies the same volume- therefore use the short cut!
Mole ratio of H2 : H2O is 2 : 2
10 000 cm3 of acid was added to the mixture. What is this in dm3?
1000cm3 = 1 dm3
10 dm3
How do you get a burette ready for titration?
- place the burette on the floor
- make sure that the tap is closed
- fill the burette with the acid/alkali using a funnel
- place a beaker under the burette and open the tap to allow the air bubble to pass
- DO NOT FORGET TO RECORD THE INITIAL VOLUME OF ACID/ALKALI BEFORE TITRATING
What is molar volume
Molar volume is the volume of one mole of gas at room temperature
Molar volume = 24 dm3 / mol
Does repeating a titration to get similar results improve the accuracy or reliablility of the results?
repeating makes the results more reliable
reliable = repeatable
How many moles are there in 24dm3 of hydrogen gas?
1 mole of hydrogen molecules
1 mole of any gas occupies 24dm3 at room temp
What is the relationship between moles, molar volume and volume of a gas?
moles = volume / molar volume
What is the equation that links concentration, moles and volume?
25.00 cm3 of sodium hydroxide was added to a conical flask. 10.0 cm3 of 2M hydrochloric acid was needed to neutralise the sodium hydroxide.
n = CV
n = 2M x 0.010 dm3 =0.02 mol of acid was used
How many moles of sodium hydroxide reacted with 0.02 mol of acid?
Use mole ratio
NaOH : HCl
1 : 1
Therefore, 0.02 moles of sodium hydroxide reacted
Why is an indicator needed during titration?
Titration uses the neutralisation of a known concentration of an acid/alkali to find the concentration of an unknown concentration of acid/alkali.
At neutralisation there are equal moles of H+ ions from the acid and OH- ions from the alkali.
An indicator is used to find this neutralisation point by providing an observable colour change.
What colour is phenolphthalein in acid?
colourless
