Help using ratios plz


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I am doing stoicheometry which deals with mole ratios of compounds in a reaction. Anyways, if the ratio is 2:7 than how would I go about getting from the number with the 2 as its ratio to the number with 7 as its ratio. example: 4.50g= the 2 x= the 7 what do I do to get to the 7 ratio.

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if you have a value of the 2 version

you do 7 divided by 2 to work out the difference thing

then multiply your value of 2 by the value you just worked out

so (RatioA/RatioB)*ValueOfA = answer

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First, you must change whatever the 4.50g substance (your example) into moles. If the reaction was 2A -> 7B and hypothetically the moles of A was 1.00 moles, then B would be half of A times 7. Once you have the moles of B, work backwards using the formula: moles = (mass / molecular mass) to find the mass of substance B, assuming you know what the molecular mass of the substance is...

Edit: Bah, i took too long ;). Yippie, 600th post :happy:

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