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1 in a sample of copper,69.1% of the atoms have a mass number of 63 and the remainder have a mass number of 65
use this information to calculate the relative atomic mass of copper...

2 a sample of sodium hydroxide solution was titrated against dilute phosphoric acid.it was found that 25.0cm3 of sodium hydroxide solution was neutralised by 12.30cm3 of phosphoric acid of concentration 0.150 mol dm-3...so:

calculate the concentration, in mol dm-3, of the sodium hydroxide solution..

2. (Original post by angelstie16)

1 in a sample of copper,69.1% of the atoms have a mass number of 63 and the remainder have a mass number of 65
use this information to calculate the relative atomic mass of copper...
The definition of Ar = the average mass of one atom when compared to the mass of a 12C isotope.

So imagine you have 100 atoms

How many of them will have a mass of 63?
How many of them will have a mass of 65?

Now work out the average.
3. (Original post by angelstie16)
2 a sample of sodium hydroxide solution was titrated against dilute phosphoric acid.it was found that 25.0cm3 of sodium hydroxide solution was neutralised by 12.30cm3 of phosphoric acid of concentration 0.150 mol dm-3...so:

calculate the concentration, in mol dm-3, of the sodium hydroxide solution..
1. Write out the balanced equation for the reaction. This gives you the ratio of the moles of each reactant.

2. Work out moles of phosphoric acid (from molarity x volume)

3. Use the mole ratio from the equation to get moles of sodium hydroxide

4. Work out concentration of NaOH (from concentration = moles/volume)
4. (Original post by charco)
1. Write out the balanced equation for the reaction. This gives you the ratio of the moles of each reactant.

2. Work out moles of phosphoric acid (from molarity x volume)

3. Use the mole ratio from the equation to get moles of sodium hydroxide

4. Work out concentration of NaOH (from concentration = moles/volume)

H3PO4 + 3NAOH- NA3PO4 + 3H2O

is my equation correct?
5. (Original post by angelstie16)
H3PO4 + 3NAOH- NA3PO4 + 3H2O

is my equation correct?
Yes, although the symbol for sodium is Na not NA
6. (Original post by angelstie16)
H3PO4 + 3NAOH- NA3PO4 + 3H2O

is my equation correct?
yes
7. (Original post by Plato's Trousers)
yes
thank you so much... both of you!
8. so did you manage to calculate the concentration of NaOH?
9. (Original post by Plato's Trousers)
so did you manage to calculate the concentration of NaOH?
yes..i did

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