Water Quality Analysis Determination Of Alkalinity Biology Essay

Alkalinity of H2O is its acid-neutralizing capacity. It is the amount of all the titratable bases. The mensural value may change significantly with the end-point pH used. Alkalinity is a step of an aggregative belongings of H2O and can be interpreted in footings of specific substances merely when the chemical composing of the sample is known.

Alkalinity is important in many utilizations and interventions of natural Waterss and effluents. Because the alkalinity of many surface Waterss is chiefly a map of carbonate, hydrogen carbonate, and hydrated oxide content, it is taken as an indicant of the concentration of these components. The mensural values besides may include parts from borates, phosphates, silicates, or other bases if these are present. Alkalinity in surplus of alkalic Earth metal concentrations is important in finding the suitableness of a H2O for irrigation.

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Alkalinity measurings are used in the reading and control of H2O and effluent intervention processes. Raw domestic effluent has an alkalinity less than, or merely somewhat greater than, that of the H2O supply. Properly runing anaerobiotic digesters typically have supernatant alkalinities in the scope of 2000 to 4000 milligram Ca carbonate ( CaCO3 ) /L.1


To find the alkalinity of the H2O sample.

To compare the alkalinity of the lake H2O and distilled H2O.



Sodium thiosulfate, 0.1 N. Dissolve 25g Na thiosulfate and dilute to 1L with distilled H2O.

Standard 0.02 N hydrochloric acid, HCL.

Phenolphthalein index: weight 5g of reagent and dissolve in 500ml of ethyl alcohol. Add 500ml of distilled H2O while stirring.

Assorted bromcresol green-methyl ruddy index. Dissolve 25g of methyl ruddy Na salt and 100mg of bromcresol green Na salt in 100ml distilled H2O.


2. 50ml of the sample measured. 1 bead of 0.1N Na thiosulfate added.

1. Samples collected utilizing the polythene bottle. The bottles filled without any air bubbles in the bottle. The aggregation analyzed every bit shortly as possible within 24 hours.

3. 2 beads of phenolphthalein index added. The colour of the solution should turn into pink. If the solution does n’t, continue to figure 4. If there is a alteration, titrated with 0.02 N HCL until the pink colour disappears and the sum of titrant used recorded.

4. Several beads of bromcresol index added. The sample titrated with 0.02 N HCL until the pH 4.5 end point where the colour alterations from blue to tap is reached. The entire volume of the acid needed to make the end point recorded.

Figure 1.0 Determination of alkalinity

Principle ANALYSIS

Alkalinity measures the acid-neutralizing capacity of a H2O sample. It is an aggregative belongings of the H2O sample and can be interpreted in footings of specific substances merely when a complete chemical composing of the sample is besides performed. The alkalinity of surface Waterss is chiefly due to the carbonate, hydrogen carbonate, and hydroxide content and is frequently interpreted in footings of the concentrations of these components. Water with higher alkalinity will hold greater the capacity to neutralize the acid. Conversely, if the alkalinity is lower, less neutralizing capacity will be needed.

The H2O sample that is used to find the alkalinity is the SST lake H2O. The H2O sample has to be taken utilizing a polythene bottle without go forthing ant H2O bubbles. This to guarantee that the H2O bubbles does non act upon the reading of the sample. The titration procedure is used to find the alkalinity of the H2O sample. Phenolphthalein index used to find the alterations of the colour of the H2O. Phenolphthalein turns colorless in acidic solution and pink in basic solution. To find the BASIC of the H2O sample from SST lake, we used the phenolphthalein to see either it changes colour to tap or non.

The colour of the solution does non turn into pink, so the bromcresol green index used. Bromcresol Green ( BCG ) is a dye of the triphenylmethane household which is used as a pH index. Then the solution titrated with 0.02 N HCL till the end point of pH 4.5 reached. Here the solution coloring material alterations from blue green to tap.





50 milliliter

50 milliliter


49.6 milliliter

47.7 milliliter


Entire alkalinity as mg/L CaCO3 = ( A + B ) x N x 50 000

milliliter sample


A= record the sum of titrant used ( A ) from No. 3

B= record the sum of titrant used ( B ) from No. 4

N= Titrate, criterion, hydrochloric acid ( HCl ) Normality

For distilled H2O,

50 milliliter

Entire alkalinity as mg/L CaCO3 = ( 0+0.4 ) x 0.02 ten 50 000

= 8 mg/ L CaCO3

For SST lake H2O,

50 milliliter

Entire alkalinity as mg/L CaCO3 = ( 0+2.3 ) x 0.02 ten 50 000

= 46 mg/ L CaCO3


From the experiment, we had obtained the alkalinity for the distilled H2O and besides the SST lake H2O. For the distilled H2O it has the alkalinity of 8 mg/L CaCO3 while SST lake H2O is 46 mg/L CaCO3.

In natural H2O, the H2O alkalinity can be determined through the beginning of H2O and the tract of the H2O flow from the beginnings. Main beginnings of H2O alkalinity are bouldery topographic points where carbonate, hydrogen carbonate and hydroxide compounds are present. These stuffs are impacting the H2O hardness which caused by Ca carbonate, CaCO3. Sometimes, CaCO3 can be referred as H2O alkalinity. Most difficult H2O contains CaCO3 which has high-buffering capacity to defy pH alterations. Area where granites or pyrogenic stones are dominant will hold lower pH with low-buffer capacity.

There are two types of indexs used in this experiment ; phenolphthalein and bromcresol green-methyl ruddy index. Phenolphthalein is used for indicant presence of hydroxide ion, OH- which phenolphthalein alkalinity is more than half of the entire alkalinity. Bromcresol is used to observe carbonate, CO32- which has less than half of the entire alkalinity.

The consequences show the entire alkalinity of the samples investigated. From the consequence, we found that the alkalinity of SST lake H2O is higher than the distilled H2O. In general, distilled H2O is impersonal solution with ph ±7.0. Distilled H2O has less mineral content than the original beginning. Compared with the SST lake H2O, the alkalinity is higher than the distilled H2O. The difference may be caused by other factors such as mineral content or organic content. For distilled H2O, the possibility of holding higher mineral or organic content is low. This will explicate the alkalinity degree of the distilled H2O. For SST lake H2O, it is possible that the mineral or organic content are higher in the H2O organic structures.

Geographically, SST lake is located at unfastened infinite surrounded with grassland, bare dirt and besides close edifices. When rains occur, the rainwater will flux on the land surface covered by flora and sedimentary stones. Topsoil of the land has weathered stones and any other organic affair. These stuffs will flux along with the rainwater to the lake sites. Calcium carbonates, CaCO3 can be found among these stuffs that flow along with the rainwater flow. CaCO3 can impact the alkalinity of the H2O since it has high-buffer capacity to defy the pH alterations in lake H2O organic structure. Open dirt or bare dirt can be found non far from the lake. There are besides beginnings of waste discharge from the nearer edifice which largely came from the research lab. The waste discharge may impact the pH of the lake H2O since different possible wastes were discharge in minimum input.

Back to the lab analysis, for both samples, we had found that coloring material alterations did non happen after assorted with phenolphthalein droplets. Form that, we knew that the pH of the samples might be lower than expected. When added with bromcresol green-methyl ruddy index and titrated with HCl, the coloring material alterations from blue into pink. After the titration, we had calculated the entire alkalinity for both samples by utilizing the expression stated in the consequence subdivision.

There are standard that had been fixed for the alkalinity of the fresh water:

Entire alkaline value ( mg/L )

Natural System


Fresh water

116 ( average value )


Based on the consequence that we had obtained, the SST Lake H2O alkalinity is 46 mg/ L CaCO3. If we compared, we had determined that the alkalinity was complied with the criterion.


In decision we had achieved all the aims for this experiment. Both samples have different alkalinity ; SST lake H2O with 46 mg/ L CaCO3 and distilled H2O with 8 mg/ L CaCO3.


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