Determination of total hardness

TITLE OF EXPERIMENT

Determination of total hardness (EDTA titrimetric method)

INTRODUCTION

All natural waters contain dissolved cations and anions. Water dissolves many ions as it flows through minerals. Although water hardness is defined as the quantity of cations with a +2 or +3 charge, calcium ion and magnesium ion are the most common of such ions in natural water. The formation of solid calcium carbonate is an endothermic process. Thus, when water containing both carbonate and calcium ions is heated, calcium carbonate can precipitate out onto the walls of pipes, boilers, and household items such as

tea pots. This can shorten the life-time of some of these items.

In addition, an insoluble scum develops when hard water comes into contact with soap. Both calcium and magnesium ions are responsible for this precipitate. This scum can be very difficult to clean. However, there is some evidence that hard water has beneficial health effects. Selenium, for example, may help prevent cancer. Soft water drinking supplies have been associated with an increased heart attack risk.

Total hardness (TH) is defined as the sum of the multivalent cations in the water. Calcium (Ca²⁺) and Magnesium (Mg²⁺) tend to be the largest components of hardness, so
TH is typically approximated as these two components.

TH = E(Multivalent cations) = Ca²⁺ + Mg²⁺

Water is classifies as soft or hard depending on the amount of hardness ions present. Surface water is generally soft fewer minerals dissolve in it. However surface water can be hard. Total hardness can be divided into two components which is carbonate hardness (CH), also known as temporary hardness and non carbonate hardness (NCH), also known as permanent hardness: TH = CH + NCH

When the hardness is numerically greater than the sum of the carbonate alkalinity and the bicarbonate alkalinity, that amount of hardness which is equivalent to the total alkalinity is called “carbonate hardness”; the amount of hardness in excess of this is called “noncarbonated hardness”. Carbonate hardness cannot be greater than total hardness. When the hardness is numerically equal to or less than the sum of carbonate and bicarbonate alkalinity, all of the hardness is “carbonate hardness” and there is no “noncarbonated hardness”. The hardness may range from 0 to 100 of mg CaCO₃/L, depending on the source and treatment to which the water has been subjected.

OBJECTIVES OF THE EXPERIMENT

To determine the total hardness (in mg CaCO₃/L) in the samples given

APPARATUS & REAGENT

Apparatus:

1. Pipette	4. Measuring cylinder (50ml, 100ml)
2. Pipette filler	5. Burette with retort stand
3. Beaker	6. Conical flask (250ml)

Reagent:

1. Eriochrome Black T indicator

2. Buffer solution

3. Standard EDTA titrant (0.01M)

4. Standard Calcium solution

METHODOLOGY

1. Chemical such as buffer solution, standard EDTA titrant (0.01M) and standard Calcium solution are prepared by the lab assistance.

2. A 25ml sample is diluted to about 50ml with distilled water in a 250ml conical flask.

3. 1ml buffer solution is added.

4. A very little of Eriochrome Black T powder is added into conical flask and the sample is mixed well.

5. The sample is titrate with standard EDTA titrant slowly, with continuous stirring until the initial red tinge color is changed into light blue color (end point).

6. The tittration is completed within 5 minutes, and is measure from time of buffer addition.

7. The volume of standard EDTA titrant used is recorded.

8. The above steps are repeated with other samples given.

Calculation:

Hardness (EDTA) as mg CaCO₃/L = (AxBx1000)/ ml Sample

A = ml titration for sample end

B = mg CaCO₃ equivalent to 1.00 ml EDTA titrant

RESULTS AND DISCUSSION

Result:

B = 1.0; ml sample = 25ml

Sample	A	B
Volume of standard EDTA titrant used (ml)	1.1	1.9
Hardness (mg CaCO3/L)	44	76

Discussion:

From the lab result, we can see that different volume of standard EDTA titrant is needed to change sample from the initial red tinge color into light blue color. Both sample A and B required 1.1ml and 1.9ml respectively to perform the changes. After perform the calculation, the total hardness of sample A is 44 mg CaCO₃/L whereas the total hardness of sample B is 76 mg CaCO₃/L.

Softening is the process of removing hardness which is one of the operations inside a water treatment plant. Ion exchange and precipitation are typical methods used. Effluent of water treatment plant always contains lower value of total hardness than influent. Therefore, sample A which contains less total hardness is effluent and sample B is the influent.

As we know, the indicator turns red when added to a solution containing Ca and Mg ions. EDTA, the titrant, complexes with Mg and Ca cations, removing them from association with the indicator. When all the Mg and Ca are complexed with EDTA, the indicator will turn blue. According to the lab result, sample A need less EDTA to change from the initial red tinge color into light blue color and its total hardness is lower than sample B. That means sample A containing less Ca and Mg ions if compared to sample B.

In our experiment, the chemical is prepared by lab assistance. During the preparation of standard calcium solution, the acidification and boiling step is needed to remove carbonates, which if present, will precipitate CaCO₃ when the solution is made basic. The precipitate obscures the end point. The excess HCl must be neutralized carefully. If too much NaOH is added, Mg(OH)₂ precipitates, giving a poor end point.

It is necessary to keep the pH of sample solution at about 10 for two reasons: (a) all reactions between metal ions and EDTA are pH dependent, and for divalent ions, solutions must be kept basic (and buffered) for the reaction to go to completion; (b) the eriochrome black T indicator requires a pH of 8 to 10 for the desired color change. If the pH of the sample solution is raised to about 13, magnesium will precipitate as the very insoluble hydroxide which will not react with EDTA.

CONCLUSIONS & RECOMMENDATIONS

Conclusion:

The total hardness of sample can be determined from this experiment. Influent and effluent from sewage treatment plant shows different value of total hardness. Both sample A and B recorded 44 mg CaCO₃/L and 76 mg CaCO₃/L respectively. Total hardness of sample A is lower than sample B. From this result, we can conclude that sample A is the effluent and sample B is the influent.

Recommendation:

1. Complete titration within 5 minutes, measured from time of buffer addition.

REFERENCES

1. http://www.bigatoll.com

2. thekrib.com/Plants/CO2/khgh.html

3. “Introduction to Environmental Engineering” (Second Edition), 2004, P. Aarne Vesilind & Susan M. Morgan, Thomson Brooks/Cole.

EXPERIMENT marshall stability and flow test for bitumen

Introduction

The Marshall stability and flow test provides the performance prediction measure for the Marshall mix design method. The stability portion of the test measures the maximum load supported by the test specimen at a loading rate of 50.8 mm/minute. Load is applied to the specimen till failure, and the maximum load is designated as stability. During the loading, an attached dial gauge measures the specimen's plastic flow (deformation) due to the loading. The flow value is recorded in 0.25 mm (0.01 inch) increments at the same time when the maximum load is recorded. The important steps are as follows;

Step 1; sample is weigh as following table;

Table 1.0; Mix ratio

Material	%	gm
20 mm aggregate	38	427.56
10mm aggregate	8	90.00
Q. Dust	52	585.00
Cement	2	22.50
Total	100 %	1125.00

g 1.0; Aggregate samples

Step 2; The sample is kept in oven to dry, till the sample reaches 150 deg C.

Fig 1.1; Dry oven

Step 3; to make the temperature rise faster, the sample was placed in fry pan and mixed well, and frequently check the temperature of the sample if it has reached 150 deg C.

Step 4; Bitumen sample is weight as following (table 2) and the aggregate and cement from the table 1 in the fry pan are been mixed .

Table 2; bitumen weight

1	4.5 %	53.00 gm
2	5.0 %	59.20 gm
3	5.5 %	65.50 gm
4	`6.0 %	71.80 gm
5	6.5 %	78.20 gm

Fig 1.2; Bitumen and aggregate sample been mixed in fry pan

Step 5; the 1^st sample is poured in to the mould after mixing it in the fry pan, and the sample is left for its temperature inside the mould has reached 130 deg C.

Step 6; When the temperature has reached 130 deg C, the sample is placed in the Marshal compactor, Marshal Compactor gives an impact load x75 times and this is done on the both sides (top and bottom).

Fig 1.3; Marshall Compactor

Step 7; Compaction process is completed, the sample is removed from the mould, and label the sample, so that it won’t be confuse with other samples.

The above steps are repeated for all the samples, after that measure the thickness of each sample, if any sample is less than 60mm consider it as failure, recode all the reading in lab table (Marshall Test results). Measure the weight of each sample in Air, Water and saturated. Before Marshall test, the sample must be place in water bath for 45 min to 1 hour at a temperature of 160 deg C.

Fig 1.4; Marshal property curve

Table 3

Marshall properties	% Bitumen contant optim curve	Critenia	Space limit
Stability	5.0	1.384	> 750 Kg
Flow	5.2	3.6	>2.0 mm
Density	5.5	2.365	-
UFB	5.2	8.0	75 % - 85 %
VIM	5.0	4.0	3% - 5%
Optimum B/contant	5.18	-	-

Experiment on Hydrostatic Pressure

Theory of experiment

The hydrostatic force on any surface is due to the fluid pressure acting on that surface. Pressure is a normal stress which is positive when in compression. Since the pressure is everywhere normal to the surface, the resultant pressure force (F_p) is also normal to the surface. The magnitude of F_p is

where p = gysin a, g = specific weight of the fluid, y = distance measured from level of zero pressure and measured in the plane of the surface, and a = angle which the plane of the surface makes with the horizontal.

Partial Immersion :

Objective of experiment

To determine the center of pressure on a partially submerged plane surface.

Apparatus

Hydraulics Bench F1-10 and Hydraulics Pressure Apparatus F1-12.

Procedure

1. The quadrant has placed on the two dowel pins and used the clamping screw, fasten

to the balance arm.

2. Measured a, L, depth d and width b of the quadrant end face.

3. The balance arm have positioned on the knife edges (pivot) with the Perspex tank on

the bench.

4. The balance pan have hanged from the end of the balance arm.

5. A length of hose is connected from the drain cock to the sump and a length from the

bench feed to the triangular aperture on the top of the Perspex tank.

6. The tank has leveled by used the adjustable feet and spirit level.

7. The counter balance weight is moved until the balance arm is horizontal.

8. Closed the drain cock and admitted water until the level reaches the bottom edge of

the quadrant. Placed a weight on the balance pan, slowly adding water into the tank

until the balance arm is horizontal.

9. The water level on the quadrant and the weight on the balance pan have recorded.

10.Fine adjustment of the water level can be achieved by overfilling and slowly draining

by used the stop cock.

11.The above for each increment of weight has repeated until the water level reaches the

top of the quadrant end face.

12.Removed each increment of weight noting weights and water levels until weights have

been removed.

Results and calculations

FILLING TANK		DRAINING TANK		AVERAGE
Weight, m(g)	Height of water, y(mm)	Weight, m(g)	Height of water, y(mm)	m	y	y2	m/y2
50 70 90 115 150	42.5 51 58.5 66.5 77.5	50 70 90 115 150	42.5 51 58.5 66.5 77.5	50 70 90 115 150	42.5 51 58.5 66.5 77.5	1806.25 2601 3422.25 4422.25 6006.25	0.028 0.027 0.026 0.026 0.025

The measurement for the equipment ;

a = 26.5 mm, b = 74 mm, d = 167 mm, L = 275 mm

Plot m/y² vs y graph. The slope of this graph should be – pb/6L and the intercept should be pb/2L (a+d) . The – pb/6L and pb/2L (a+d) is theory part.

Experiment Part

Let a₁ = slope of the graph let b₁ = intercept for the graph

= - 0.0015/20 = 0.039 g/mm²

= - 7.5 x 10^-5 g/mm³

Theory Part

Since the theory and experiment result are different, it should to find out the percentage different between them by using following formulas :

Discussion of results

From the results obtained, the slope for the graph is -7.5 x 10^-5 g/mm³ and the intercept is 0.039g/mm². However for the theoretical result for the slope is -4.485 x 10^-5g/mm³ and the intercept is 0.026 g/mm². For the normal situation, the slope and the intercept for experiment part should be same with the theoretical part. If even there are different, but if the different percentage is not more than 10 %, the results still can be accepted.

For this experiment, after obtained the different percentage between the theoretical part and experiment part, is found that the different for the slope between both side is 67.22% and the different for the intercept between both side are 50%. So that the different between both site is more than 10 %, this lab results not acceptable.

There are so much differences between theoretical and experimental part caused by human error. This can be occurred because when taking the reading, it only use eyes look at the reading directly and not by some apparatus which is more accuracy. This laboratory results out of the range from normal situation also caused by mistake when filling water and draining water from the tank.

Conclusion

From the experiment done, it is a way to determine centre of pressure. This laboratory is considered not well but laboratory test sometimes will not success. It may caused by many reasons.