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Help with moles calculations!

Could anyone show me how to do part 2 in the question of the image attached? I have worked out the answer to part 1 as being 9.894 * 10^-4!

^{The answer to part 2 is 148 (3sf) but I have no idea how to work it out!}

^{Please help!}

Screen Shot 2017-05-02 at 14.31.32.png125.7KB

Reply 1

charco

Study Forum Helper

Original post by dp00

Once you have the moles of bicarbonate in 250ml of solution and the question gave you the mass which was originally dissolved you use the equation:

moles = mass/Mr

to find the Mr

Reply 2

username2315623

Original post by charco

Once you have the moles of bicarbonate in 250ml of solution and the question gave you the mass which was originally dissolved you use the equation:

moles = mass/Mr

to find the Mr

Thank you!

How do you calculate the moles of bicarbonate though? You have to use (conc*volume)/1000 right? What are the values for conc and volume and how do you find them?

Sorry!

Reply 3

charco

Study Forum Helper

Original post by dp00

Thank you!

How do you calculate the moles of bicarbonate though? You have to use (conc*volume)/1000 right? What are the values for conc and volume and how do you find them?

Sorry!

From the moles of acid used in the titration and the equation for the reaction, remembering to scale it up for the 250 ml solution

Reply 4

tony_dolby

Original post by dp00

Thank you!

How do you calculate the moles of bicarbonate though? You have to use (conc*volume)/1000 right? What are the values for conc and volume and how do you find them?

Sorry!

You find moles of bicarbonate from the chemical equation. You know the moles of acid from part a) and this reacts 1:1 with the bicarbonate. You now know the moles of bicarbonate ( the same number!) in 25 cm3. How many moles are there in the original 250cm3? Ten times as many!

Now you can use the mass of the bicarbonate and the moles to work out the Mr.