Mass Mass

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Mass Mass

• Ch 8 Blue Book

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• Mass-Mass problems are done when we want to find
  the amount of a compound made from a known amount
  of another compound.
• Stoichiometry

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Example

• Zinc metal and hydrochloric acid react to form
  zinc chloride and hydrogen gas. How many grams
  of H2 are made from 10.0 g HCl?
• Step 1 Write out and balance the chemical
  equation.
• Zn 2HCl ? ZnCl2 H2
• Step 1.5 identify your known and unknown, draw
  an arrow going from your known amount to your
  unknown amount.

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• Step 2 Convert grams of given ? mols
• Step 3 Determine mole to mole ratio from
  balanced equation convert moles of given to
  moles of required (unknown amt. you are trying to
  find)
• Step 4 Convert moles of required (unknown)?
  grams

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• Zinc metal and hydrochloric acid react to form
  zinc chloride and hydrogen gas. How many grams
  of H2 are made from 10.0 g HCl?
• Zn 2HCl ? ZnCl2 H2
• Answer 0.27 g H2

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Example

• Calculate the grams of NaOH required to produce
  15.0 grams of Na2SO4 by the neutralization of
  NaOH with excess H2SO4.
• Step 1 Write Balance Equation
• Step 1.5 I.D. known unknown
• Step 2 mass of known ? mols of known
• Step 3 mols of known ? mols of unknown
• (Stoichiometric Ratio)
• Step 4 mols of unkown ? mass of unknown

8.45 g NaOH
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Example

• Washing soda (sodium carbonate decahydrate) is a
  hydrated compound used for washing, water
  softening and bleaching. If a sample of sodium
  carbonate decahydrate has a mass of 20.0 grams
  and 10.0 of this 20.0 gram sample is inert, what
  mass of sodium carbonate will be left when the
  material is heated to drive off the water of
  hydration?

6.67 g Na2CO3
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HW Assignment

• 1-8 Due 4/8 pg. 79
• 9-16 Due 4/10 pgs. 82-83