Mixtures of 50 g of ZnO-TiO_2 are each shaken with 250 ml of water and allowed t
ID: 531781 • Letter: M
Question
Mixtures of 50 g of ZnO-TiO_2 are each shaken with 250 ml of water and allowed to settle. After 14 days of equilibration, it is found that the sediment volume is 1.65 times larger when the weight ratio of ZnO to TiO_2 is 1.0 than when the ratio is 100. Some particle characteristics are the following: a. Assuming the particles are uniform spheres, calculate the ratio for the number of particles of ZnO to TiO_2 for each of the weight ratios given. b. Propose an explanation for the more voluminous sediment that results when the weight ratio is 1.0 than when it is 100.Explanation / Answer
Answer b) Density 1=M1/V1
density2=M2/V2
Density1/Density 2=M1/M2*V2/V1
Density is inversely proportional to volume and directly proportion to Mass
As weight ratio increases density increases and volume decreases.Hence we get more voluminous sediment when weight ratio is 1 .
OR
Weight ratio= Mass of solute/mass of solvent
Mass of ZnO=50g
Mass of TiO2=50g
Mass of water =250ml=250g
Weight ratio of ZnO =50/250=1/5
Weight ratio of TiO2 =50/250=1/5
Weight ratio of ZnO to TiO2=1
Sediment volume =1.65
Density=Mass /volume=1g/1.65g=0.61
When weight ratio is 100,Density=100g/1.65g=60.61
As density increases volume decreases.so when weight ratio or mass is small,density decreases and sedimentation volume increases
Answer a)
(Volume=Mass/Density=81.38g/5.6g/cm3=14.53cm3
so 6.022*1023 molecules of ZnO has volume 14.53cm3)
1mole of ZnO=81.38g=6.022*1023molecules of ZnO
50g of ZnO is 50/81.38moles ZnO=0.61moles of ZnO=6.022*1023*0.61 =3.673*1023 molecules of ZnO
(Radius of TiO2=2.2/2=1,1cm
Volume of TiO2 =4/3R3=4/3*3.14*1.13=5.572
so 6.022*1023 molecules of ZnO has volume 5.572cm3)
1mole of TiO2 =79.86g=6.022*1023molecules of TiO2
50g of TiO2=50/79.86=0.627moles of TiO2=3.77*1023 molecules of TiO2
When weight ratio is 1,
Particle ratio =No of particles of ZnO/No of particle of TiO2=3.67/3.77=0.97
When weight ratio is 100,
Particle ratio =3.67*100/3.77=100