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# Calculations watch

1. I'm a bit stuck on these two questions, can someone please explain how I can go about figuring them out. Thanks.

1. A 7 % solution of sodium chloride is diluted by using 1 part of it and mixing it with 4 parts of water. What is the concentration (%) of the diluted solution?

2. How many mg of substance should be weighed out to prepare 50cm3 of a 0.86% solution
2. For Q1 it may help to give numbers to the "parts", e.g. say 1 part is 100 milliliters. Then you can find how many ml of sodium you have in 1 part of solution. Then you add four parts water (400ml), so total volume is now 500 ml. You can divide the sodium by the total , and multiply by 100, to get percentage.

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