Multiple+conversions+between+moles,mass,+volume+and+number+of+particles

[|20100617671.jpg]Type in the content of your page here.


 * __ Multiple conversions between mass, volume and number of particles __

Find the number of atoms in a given number of molecules.( two steps) ** //Step a) Count the number of atoms in one molecule. // //Step b) Multiply the number of molecules //

//**a) **// the number of atoms in 1 molecule. N: N×2=2 H: H×4×2=8 S: S×1=1 O: O×4=4 Total atoms in 1 molecule has 2+8+1+4=15 //**b **////) // there are 3 molecules 15×3=45 Therefore, there are 45 atoms in 3molecules of (NH 4 ) 2 SO 4
 * Example 1: **
 * How many atoms are in 3 molecules of (NH **** 4 **** ) **** 2 **** SO **** 4 **

//Step // //a) Count the number of the atoms that you need to find in 1 molecule. // //Step b) Multiply the number of molecules . //
 * Find a part of atoms in a given number of molecules. **

**Example 2: ** **//a //**//) // H: H×4×2=8 Total atoms in 1 molecule of hydrogen atoms are 8 //**b **////) // there are 3 molecules 8×3=24 Therefore, there are 24 hydrogen atoms in 3 molecules of (NH 4 ) 2 SO 2  ­of molecules.
 * <span style="font-family: 'Calibri','sans-serif'; font-size: 14pt;">How many hydrogen atoms are in 3 molecules of (NH ****<span style="font-family: 'Calibri','sans-serif'; font-size: 8pt;">4 ****<span style="font-family: 'Calibri','sans-serif'; font-size: 14pt;">) ****<span style="font-family: 'Calibri','sans-serif'; font-size: 8pt;">2 ****<span style="font-family: 'Calibri','sans-serif'; font-size: 14pt;">SO­ ****<span style="font-family: 'Calibri','sans-serif'; font-size: 8pt;">4 **

single step conversion

1 mole/6.02×10^23 particles ** || 1 mole/(molar mass)g ** || 1 mole/ 22.4L ** || 1 molecule/(atoms count)atoms** ||
 * **<span style="font-family: 'Arial','sans-serif'; font-size: 14pt;">conversion ** || **<span style="font-family: 'Arial','sans-serif'; font-size: 14pt;">Conversion factor ** ||
 * ** <span style="font-family: 'Arial','sans-serif';">Moles <span style="font-family: 宋体;">←→ <span style="font-family: 'Arial','sans-serif';">Number of particles ** || ** 6.02×10^23particles/1 mole
 * **<span style="color: #008000; font-family: 'Arial','sans-serif';">Moles ←→ Mass ** || ** (molar mass)g/1 mole
 * ** <span style="font-family: 'Arial','sans-serif';">Moles ←→ Volume ( //<span style="font-family: 'Arial','sans-serif'; font-size: 9pt;">gases at STP //<span style="font-family: 'Arial','sans-serif';">) ** || ** 22.4L / 1 mole
 * **<span style="color: #008000; font-family: 'Arial','sans-serif';">Molecules ←→Atoms ** || (**atoms count)atoms/1 molecule

Example: //**1) How many molecules are there in 5 moles of molecules?**// number of molecules= 5 moles ×(6.02 ×10^23 particles/1 mole) = 3.01×10^24 molecules

1) Molar mass of H 2 O= 2H=2×1.0=2.0g, 1O=1×16.0=16.0g 2.0g+16.0g=18.0g 2) number of mass of H 2 O= 3 moles ×(18.0gH 2 O/1moleH 2 O)=54.0gH 2 O
 * //2) What is the mass of H//** **//2//** **//O in 3 moles?//**

number of litres =0.5mol SO 2 ×(22.4L SO 2 /1mol SO 2 )=12.2L SO 2
 * //3) What is the volume occupied by 0.5 mol of SO//** **//2//** **//(g) at STP?//**

number of atoms =7 molecules H 3 PO 4 ×(8 atoms of H 3 PO 4 /1 molecule H3PO4)=56 atoms H 3 PO 4
 * // 4) How many atoms are there in 7 molecules of H 3 PO 4 //** **//?//**

**__In the calculations, some questions should use conversions more than once; however, mole is in the centre, because all conversions between mass, particles and volume should be converted to mole at first.__ These are some general calculations steps. //Particles ←→ mass://** //Convert particles ←→ moles(using 6.02×10^23/1 mole) ←→ mass( using molar mass/1 mole)// //**Particles ←→ volume:** Convert particles←→ moles(using 6.02×10^23/1 mole) ←→ volume(using 22.4L/1 mole at STP)// //**Mass to volume:** Convert mass←→ moles(using molar mass/1 mole) ←→ volume(using 22.4L/1 mole at STP)// <span style="font-family: 'Arial','sans-serif'; font-size: 14pt;"> **Example 1:** //** What is the volume occupied by 40.0g of O2 (g) at STP **// Plan: convert Mass to Moles then to Volume mass×(1 mole/ molar mass)×(volume/ 1 mole) 1) molar mass: 2O: 2×16.0g= 32.0g O 2  2) 40.0g O  2 ×(1 mole O 2 / 32.0g O 2 )×(22.4L O 2 / 1 mole O 2 )=28.0L O 2

**Example 2:** // **What is the mass of 3.00×10^18 atoms of Fe?** // Plan: convert # of atoms to Moles then to Mass mass= number of atoms ×(1 mole/ 6.02×1023 atoms) ×(molar mass/ 1 mole) 1) Molar mass: 1Fe= 1×55.8g= 55.8g Fe 2) Mass=3.00×10^18 atoms Fe×(1 mole Fe/6.02×10^23 Fe)×(55.8g Fe/1 mole Fe)=2.78g Fe

<span style="color: #ff00b3; font-family: 'Calibri','sans-serif'; font-size: 14pt; font-weight: normal;">//a) if the density is mentioned at a point in a problem, we should use d=m/v. b) If the volume of a solid or liquid is unknown, calculate the volume from v=m/d c) If the mass is unknown, calculate the mass from m=v×d//
 * __22.4L/1 mole used all refer to gases at STP, but if the density is mentioned at a point in a problem, we should use d=m/v.( three situation)__ **

**Example 1:** **//What is the volume occupied by 4.00 mole of Al203? (d=3.97g/ml)//** Hint : density relates to volume to mass, mass is relates to moles. number of ml= mole ×(molar mass/1 mole)×(1 ml/3.97g) 1) Molar mass:2Al=2×27.0g=54.0g, 3O=3×16.0g=48.0g 54.0g+48.0g=102.0g 2) number of ml= 4.00ml Al203×(102.0g Al203/1 mol Al203)×(1 ml Al203/3.97g Al203)=102.8ml Al203

Plan: convert volume to mass, then to moles, then to Avogadro’s number, finally to number of atoms number of atoms= volume×density×(1mole/molar mass)×(6.02×10^23 molecule/1 mole) ×(atoms count/1 molecule) number of atoms=200ml×(3.97g/1ml)×(1mole/102.0g)×(6.02×10^23molecules/1mole)×(2Al atoms/1 molecule)=9.37×10^23 atoms
 * Example2:**
 * // How many atoms of Al are in 200 ml of Al2O3? (d=3.97g/ml) //**