document.write( "Question 498280: Given a stock solution of 5.0% sodium chloride (NaCl), how would you prepare 20 ml of a 2.0% sodium chloride solution? (I have tried many of the examples you give others but I can't work it out for some reason.) \n" ); document.write( "

Algebra.Com's Answer #336995 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
In words:
\n" ); document.write( "(ml of NaCl you end up with) / (ml of total solution you end up with) = 2%
\n" ); document.write( "They are not telling you how many ml of the stock solution you start with.
\n" ); document.write( "They only say you end up with 20 ml of solution.
\n" ); document.write( "In order to get down from 5% to 2% you must add water ( or whatever the solvent is)
\n" ); document.write( "They should have mentioned that
\n" ); document.write( "Let $\"a\"$ = ml of the 5% solution you need
\n" ); document.write( "Let $\"b\"$ = ml of water to add
\n" ); document.write( "given:
\n" ); document.write( " $\"+.05a+\"$ = NaCl in the 5% solution
\n" ); document.write( "(1) $\"+a+%2B+b+=+20+\"$
\n" ); document.write( "---------------
\n" ); document.write( "(2) $\".05a+%2F+20+=+.02+\"$
\n" ); document.write( "(2) $\"+.05a+=+.4+\"$
\n" ); document.write( "(2) $\"+a+=+8+\"$
\n" ); document.write( "and, since
\n" ); document.write( "(1) $\"+a+%2B+b+=+20+\"$
\n" ); document.write( "(1) $\"+8+%2B+b+=+20+\"$
\n" ); document.write( "(1) $\"+b+=+12+\"$
\n" ); document.write( "You need 8 ml of the 5% solution
\n" ); document.write( "and 12 ml of water
\n" ); document.write( "check:
\n" ); document.write( "(2) $\".05a+%2F+20+=+.02+\"$
\n" ); document.write( "(2) $\".05%2A8+%2F+20+=+.02+\"$
\n" ); document.write( "(2) $\"+.4%2F20+=+.02+\"$
\n" ); document.write( "(2) $\"+.4+=+.4+\"$
\n" ); document.write( "OK \n" ); document.write( "

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