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Math Help - Acid/Salt math

  1. #1
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    Acid/Salt math

    a) how high is the salt in a solution of 800g water, 50g alt and 500g 2,5 saltsolution?

    b) A detergent that is bought 20% strong and is going to be thinned to the proportion 3:50. What strenght does the ready detergent have?

    c) How much 45% acid must be pourd into 500ml 12% acid to make a 30% acid?



    Whole calculations and answers please iw been hitting my head in the wall for 2 days now.
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  2. #2
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    Quote Originally Posted by Rambo View Post
    a) how high is the salt in a solution of 800g water, 50g alt and 500g 2,5 saltsolution?

    b) A detergent that is bought 20% strong and is going to be thinned to the proportion 3:50. What strenght does the ready detergent have?

    c) How much 45% acid must be pourd into 500ml 12% acid to make a 30% acid?
    to a) I assume that the "2,5 saltsolution" is actually 2.5% saltsolution. If so:

    Calculate the total amount of salt:

    50 g + 2.5% * 500 g = 50 g + 12.5 g = 62.5 g

    Calculate the total mass:

    800 g + 50 g + 500 g = 1350 g

    Therefore you have the ratio \frac{salt}{total\ mass} = \frac{62.5}{1350} = 0.046296.. \approx 4.63\%

    to b) For convenience I use grams:

    Calculate the total amount of detergent in 3 g of the 20%-solution:

    \frac{20}{100} \cdot 3 = 0.6\ g of detergent.

    The total mass of the thinned solution is 53 g (You added 50 g to the original 3 g of concentrated detergent)

    Therefore you have the ratio \frac{detergent}{total\ mass} = \frac{0.6}{53} = 0.01132.. \approx 1.13\%


    to c) Let V denote the unknown volume of the 45%-acid.

    Calculate the total amount of acid:

    0.45 \cdot V + 0.12 \cdot 500 = 0.3\cdot (500+V)

    0.45 \cdot V + 0.12 \cdot 500 = 0.3\cdot 500+0.3 \cdot V . Collect all terms with V at the LHS, all constants at the RHS:

    V(0.45 - 0.3) = 150 - 60~\iff~ V = 600
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  3. #3
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    Quote Originally Posted by earboth View Post
    to a) I assume that the "2,5 saltsolution" is actually 2.5% saltsolution. If so:

    Calculate the total amount of salt:

    50 g + 2.5% * 500 g = 50 g + 12.5 g = 62.5 g

    Calculate the total mass:

    800 g + 50 g + 500 g = 1350 g

    Therefore you have the ratio \frac{salt}{total\ mass} = \frac{62.5}{1350} = 0.046296.. \approx 4.63\%

    to b) For convenience I use grams:

    Calculate the total amount of detergent in 3 g of the 20%-solution:

    \frac{20}{100} \cdot 3 = 0.6\ g of detergent.

    The total mass of the thinned solution is 53 g (You added 50 g to the original 3 g of concentrated detergent)

    Therefore you have the ratio \frac{detergent}{total\ mass} = \frac{0.6}{53} = 0.01132.. \approx 1.13\%


    to c) Let V denote the unknown volume of the 45%-acid.

    Calculate the total amount of acid:

    0.45 \cdot V + 0.12 \cdot 500 = 0.3\cdot (500+V)

    0.45 \cdot V + 0.12 \cdot 500 = 0.3\cdot 500+0.3 \cdot V . Collect all terms with V at the LHS, all constants at the RHS:

    V(0.45 - 0.3) = 150 - 60~\iff~ V = 600

    Could someone show me the last calcultation how earboth got to v=600. I know im stupid but i dont get it but i want to because i have exam on friday.
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