Determining unknown quantities question
Anyone know the answer to this? It was in one of the multiple choice tests we were given online. I got the answer wrong and was given the correct answer (3) but not any of the working out so I don't know how to reach the answer.
Read the information below about an acid represented by the formula HxY.
•One mole of the acid represented by HxY ionises to produce x mol of hydrogen ions.
•The molar mass of the acid is 192 g mol−1.
•2.4 g of the acid was dissolved in water and the volume made up to 250 cm3.
•20 cm3 of this solution was neutralised by exactly 25.0 cm3 of a 0.12 mol dm−3 solution of NaOH(aq).
What is the value of x?
Thanks
Read the information below about an acid represented by the formula HxY.
•One mole of the acid represented by HxY ionises to produce x mol of hydrogen ions.
•The molar mass of the acid is 192 g mol−1.
•2.4 g of the acid was dissolved in water and the volume made up to 250 cm3.
•20 cm3 of this solution was neutralised by exactly 25.0 cm3 of a 0.12 mol dm−3 solution of NaOH(aq).
What is the value of x?
Thanks
Hi,
Since the Mr is 192g, you can find the number of moles in your 250 cm^3 solution by doing 2.4/192. This gives you 0.0125 moles.
Since you are only using 20cm^3 of your solution, you multiply 0.0125 by 20/250 to find the number of moles present in your 20cm^3 solution. This comes to 1 x 10^-3 moles
Then workout the no. moles of NaOH with vol x conc, which gives you 3 x 10^-3 moles. You then have a molar ratio of HxY: NaOH, 1:3.
Therefore your reaction must be HxY + 3NaOH --> 3NaY + 3H20. Hence, your x value must be 3.
Hope this helps
Since the Mr is 192g, you can find the number of moles in your 250 cm^3 solution by doing 2.4/192. This gives you 0.0125 moles.
Since you are only using 20cm^3 of your solution, you multiply 0.0125 by 20/250 to find the number of moles present in your 20cm^3 solution. This comes to 1 x 10^-3 moles
Then workout the no. moles of NaOH with vol x conc, which gives you 3 x 10^-3 moles. You then have a molar ratio of HxY: NaOH, 1:3.
Therefore your reaction must be HxY + 3NaOH --> 3NaY + 3H20. Hence, your x value must be 3.
Hope this helps
Thanks, that's great! I knew I was missing a step, turns out I forgot to multiply to find the amount of moles in 20cm^3 rather than 250. Thanks again
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