Step 6: Iterate design if needed CE 360 Quiz 4 Learning Objectives Quiz 4 will b

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Step 6: Iterate design if needed CE 360 Quiz 4 Learning Objectives Quiz 4 will be held at the beginning of lesson 15 (Monday) Assigned reading to stay current with this class: read through all of chapter 6 sections 1-4 and part of 6-5 by Monday. Remember that all these questions have simple answers that can be explained in just a phrase or two or a short equation. g lime-soda softening: calcium or magnesium? Explain why it is cheaper. 2. Label the saturation state of a solution (identify whether or not precipitation will occur) given a precipitation reaction equation with solubility constant and the concentrations of two ions. Note: be familiar with the rules of adding exponents when multiplying (eg. 10* x 10 10) 3. Name one commonly used coagulant. 4. Contrast type I and type II sedimentation. 5. Explain which of the following metal ions would make a better coagulant: Na* or Fe? 6. Describe the effect of adding ferric chloride to water on alkalinity and pH. 7. Explain why a gentle mixing is used during the flocculation p 8 Name the term used to quantify the degree of mixing. rocess. Why not rapid mixing? 9. Name the variables vo and v,. Note that vo has a few valid names, all of which are acceptable. 10. Write an equation to calculate vo based on sedimentation tank geometry and flowrate. Hint, vo is actually Directed reading for sections 6-4 and 6-5 to come prepared for Monday's class: equal to the 'water velocity

Explanation / Answer

Solutions:

Ans3- A commonly used coagulant is Alum ( Al2(SO4)3 .14H2O )

Ans4- Type 1 settling is mainly related with discrete particle settling. They settle individually under the action of gravity without any interaction with subsequent or adjacent particles

Type 2 settling is known as flocculant settling.Here small particles join with each other to form larger blocks called flocs to settle down.the resulting particle has a greater mass.

Ans 5- Mainly all coagulants are either aluminium or iron based. So in this comaparison Fe is more preferrable.Used in calcium alkalinity, Also normally, multivalent cations are used whereas Na is monovalent.But ferrous ions are used where excess solubility is of greater importance.

Ans 6-

2FeCl3 + 3Ca(HCO3)2 = 2Fe(OH)3 +3CaCl2 + 6CO2

for highly alkaline water , the amount of Fecl3 might be increased to lower the pH to the optimal pH range for Fe which is 5.5-6.5.

as a result the alkalinity will also decrease.

Ans 7- As flocculation is a process of agglomeration of destablized particles into a larger one, it requires time.Gentle mixing helps in developing contact between the surfaces of these particles.Thus the number of particles colliding with each other would also increase.

Ans 8- One of the term used to quantify the degree of mixing is Homogeneity

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