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4. How many moles of gold (Au) are in a pure gold nugget having a mass of 25.0 grams.

Sagot :

Space

Answer:

0.127 mol Au

General Formulas and Concepts:

Math

Order of Operations: BPEMDAS

  1. Brackets
  2. Parenthesis
  3. Exponents
  4. Multiplication
  5. Division
  6. Addition
  7. Subtraction
  • Left to Right

Chemistry

Atomic Structure

  • Reading a Periodic Table
  • Moles

Stoichiometry

  • Using Dimensional Analysis

Explanation:

Step 1: Define

[Given] 25.0 g Au

[Solve] moles Au

Step 2: Identify Conversions

[PT] Molar Mass of Au - 196.97 g/mol

Step 3: Convert

  1. [DA] Set up:                                                                                                     [tex]\displaystyle 25.0 \ g \ Au(\frac{1 \ mol \ Au}{196.97 \ g \ Au})[/tex]
  2. [DA] Multiply/Divide [Cancel out units:                                                          [tex]\displaystyle 0.126923 \ mol \ Au[/tex]

Step 4: Check

Follow sig fig rules and round. We are given 3 sig figs.

0.126923 mol Au ≈ 0.127 mol Au

Sarah06109

Answer:

[tex]\boxed {\boxed {\sf 0.127 \ mol \ Au}}[/tex]

Explanation:

To convert from mass to moles, the molar mass must be used. This can be found on the Periodic Table.

  • Gold (Au): 196.96657 g/mol

Use this number as a ratio.

[tex]\frac {196.96657 \ g\ Au }{1 \ mol \ Au}[/tex]

Multiply by the given number of grams.

[tex]25.0 \ g \ Au*\frac {196.96657 \ g\ Au }{1 \ mol \ Au}[/tex]

Flip the fraction so the grams of gold will cancel.

[tex]25.0 \ g \ Au*\frac {1 \ mol \ Au}{196.96657 \ g\ Au }[/tex]

[tex]25.0*\frac {1 \ mol \ Au}{196.96657 }[/tex]

[tex]\frac {25.0 \ mol \ Au}{196.96657 }[/tex]

[tex]0.1269250919 \ mol \ Au[/tex]

The original measurement has 3 significant figures, so the answer must have the same. For the number we calculated that is the thousandth place. The 9 in the ten thousandth place tells us to round the 6 to a 7.

[tex]0.127 \ mol \ Au[/tex]

25.0 grams of gold is about 0.127 moles of gold.

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