{"id":19514,"date":"2018-01-31T05:37:54","date_gmt":"2018-01-31T05:37:54","guid":{"rendered":"https:\/\/cbselibrary.com\/?p=19514"},"modified":"2020-11-25T17:19:47","modified_gmt":"2020-11-25T11:49:47","slug":"cbse-class-10-science-lab-manual-ph-samples","status":"publish","type":"post","link":"https:\/\/cbselibrary.com\/cbse-class-10-science-lab-manual-ph-samples\/","title":{"rendered":"CBSE Class 10 Science Lab Manual – pH of Samples"},"content":{"rendered":"
AIM MATERIALS REQUIRED<\/span><\/strong> THEORY<\/span><\/strong> <\/p>\n Pure water is neutral because of the absence of free ions. A paper impregnated with the universal indicator is used for measuring pH. Now-a-days, pH meter, an electronic device, is used to measure the pH. pH is defined as the negative logarithm of hydrogen ion concentration in moles per litre. The pH value has no unit. It can be written as:<\/p>\n pH = -log[H+<\/sup>] or pH = – log [H3<\/sub>O+<\/sup>]<\/strong><\/p>\n pH Paper<\/strong> Note:<\/strong> Violet\/blue colour indicates alkaline solution, red\/pink colour indicates acidic solution and green colour indicates neutral solution.<\/p>\n PROCEDURE<\/span><\/strong><\/p>\n OBSERVATION AND INFERENCE<\/strong> \u00a0RESULT\/CONCLUSION<\/strong><\/span> PRECAUTIONS<\/span><\/strong><\/p>\n Viva – Voce<\/span><\/strong><\/p>\n Question 1.<\/span><\/strong> Question 2.<\/span><\/strong> Question 3.<\/span><\/strong> Question 4.<\/span><\/strong> Question 5.<\/span><\/strong> Question 6.<\/span><\/strong> Question 7.<\/span><\/strong> Question 8.<\/span><\/strong> Question 9.<\/span><\/strong> Question 10.<\/span><\/strong> Question 11.<\/span><\/strong> Question 12.<\/span><\/strong> Question 13.<\/span><\/strong> Question 14.<\/span><\/strong> Question 15.<\/span><\/strong> Question 16.<\/span><\/strong> Science Lab Manual<\/a>Science Practical Skills<\/a>Science Labs<\/a>Math Labs<\/a>Math Labs with Activity<\/a><\/p>\n","protected":false},"excerpt":{"rendered":" CBSE Class 10 Science Lab Manual – pH of Samples AIM To find the pH of the following samples by using pH paper\/universal indicator Dilute hydrochloric acid (HCl) Dilute sodium hydroxide (NaOH) solution ? Dilute ethanoic acid (CH3COOH) solution Lemon juice Water (H2O) Dilute sodium bicarbonate (NaHCO3) solution MATERIALS REQUIRED Six test tubes, test tube … Read more<\/a><\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":""},"categories":[6805],"tags":[],"yoast_head":"\n
\n<\/strong><\/span>To find the pH of the following samples by using pH paper\/universal indicator<\/p>\n\n
\nSix test tubes, test tube stand, glass rod, pH paper, dropper, standard pH colour chart, universal indicator, sample of solution\u2014dilute HCl, dilute NaOH, dilute CH3<\/sub>COOH, dilute NaHCO3<\/sub>, water, lemon juice.<\/p>\n
\nThe pH Scale<\/a><\/strong>
\nIt is a scale used for measuring hydrogen ion concentration. The p in the pH stands for potenz which means power in German. It has values 0 (very acidic) to 14 (very alkaline). pH is a number which indicates the acidic or basic nature of a solution (as shown in Fig. 1).
\nHigher the hydronium ion concentration present in the solution, lower is its pH value. [pH means power of hydrogen ions]<\/p>\n\n
\npH of a solution can be determined by using pH paper. When the pH paper is dipped in the solution whose pH is to be found out, a colour is developed on the pH paper. The colour is matched with the standard colour chart (as shown in Fig. 2).
\n
\nIn the place of pH paper, we can use universal indicator solution or universal indicator paper to measure the pH. When we take a drop of the test solution and place it on universal indicator paper, the paper turns a particular colour. The colour of the indicator paper is then matched against a colour chart showing the pH value for different colours. Universal indicator is also available in the form of solution.
\nThe colours produced by universal indicator at different pH values are given in table below.<\/p>\n\n\n
\n pH<\/strong><\/td>\n Colour<\/strong><\/td>\n pH<\/strong><\/td>\n Colour<\/strong><\/td>\n pH<\/strong><\/td>\n Colour<\/strong><\/td>\n<\/tr>\n \n 0<\/td>\n Dark red<\/td>\n 5<\/td>\n Orange-yellow<\/td>\n 10<\/td>\n Dark blue<\/td>\n<\/tr>\n \n 1<\/td>\n Red<\/td>\n 6<\/td>\n Green-yellow<\/td>\n 11<\/td>\n Purple<\/td>\n<\/tr>\n \n 2<\/td>\n Light red<\/td>\n 7<\/td>\n Green<\/td>\n 12<\/td>\n Dark purple<\/td>\n<\/tr>\n \n 3<\/td>\n Orange-red<\/td>\n 8<\/td>\n Green-blue<\/td>\n 13<\/td>\n Light violet<\/td>\n<\/tr>\n \n 4<\/td>\n Orange<\/td>\n 9<\/td>\n Blue<\/td>\n 14<\/td>\n Violet<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n
\n<\/li>\n
\n<\/li>\n
\n<\/span><\/p>\n\n\n
\n S.No.<\/strong><\/td>\n Sample solution<\/strong><\/td>\n Observation<\/strong>
\n (Colour produced on pH paper)<\/strong><\/td>\nInference<\/strong>
\n (Approximate pH)<\/strong><\/td>\n<\/tr>\n\n 1.<\/td>\n Dilute HCI<\/td>\n <\/td>\n <\/td>\n<\/tr>\n \n 2.<\/td>\n Dilute NaOH<\/td>\n <\/td>\n <\/td>\n<\/tr>\n \n 3.<\/td>\n Dilute CH3COOH<\/td>\n <\/td>\n <\/td>\n<\/tr>\n \n 4.<\/td>\n Lemon juice<\/td>\n <\/td>\n <\/td>\n<\/tr>\n \n 5.<\/td>\n Water<\/td>\n <\/td>\n <\/td>\n<\/tr>\n \n 6.<\/td>\n Dilute NaHC03<\/sub><\/td>\n <\/td>\n <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\nThe pH of the given samples by using pH paper are as follows:<\/p>\n\n
\n
\nWhat do you mean by pH? [NCERT]<\/strong>
\nAnswer:<\/strong><\/span>
\nThe pH is the measure of the acidic (or basic) power of a solution. It is a scale for measuring hydrogen ion concentration in a solution. Higher the hydronium ion concentration in the solution, lower is their pH values.<\/p>\n
\nWhat is the pH of pure water at 25\u00b0C (298 K)? [NCERT]<\/strong>
\nAnswer:<\/strong><\/span>
\nThe pH of pure water at 25\u00b0C is equal to 7.<\/p>\n
\nWhat according to you should be the pH of dil. HCI and dil. NaOH solution? Observe and explain your findings. [NCERT]<\/strong>
\nAnswer:<\/strong><\/span>
\npH of dilute HCI is found to be 2 and pH of dilute NaOH is 14. Solutions with pH = 0 to 3 are strongly acidic, so dilute HCI is a strong acid. And the solution with pH = 12 to 14 are strongly basic, so dilute NaOH solution is a strong base.<\/p>\n
\nOn opening the soda water bottle the dissolved CO2<\/sub> comes out, would the pH of the solution increase or decrease as the gas comes out ? Explain your answer. [NCERT]<\/strong>
\nAnswer:<\/strong><\/span>
\nThe pH of the solution will increase as the gas comes out and the solution becomes less acidic.<\/p>\n
\nHow is the concentration of hydronium ions (H3<\/sub>O+<\/sup>) affected, when a solution of an acid is diluted?
\nAnswer:<\/strong><\/span>
\nOn dilution of an acid, the concentration of hydronium ions (H3<\/sub>O+<\/sup>) per unit volume decreases.<\/p>\n
\nSolid sodium bicarbonate was placed on a strip of pH paper. What colour would you observe on a strip of pH paper?
\nAnswer:<\/strong><\/span>
\nThe colour on a strip of pH paper would not change. (Since, an acid or base shows their nature in aqueous state only and not in solid or pure state, hence solid sodium bicarbonate does not affect the colour of pH paper).<\/p>\n
\nWhat effect does the concentration of H+<\/sup> (aq) have on the acidic nature of the solution?
\nAnswer:<\/strong><\/span>
\nHigher the concentration of H+<\/sup> ions in a solution, more acidic is the solution.<\/p>\n
\nA student was given four unknown colourless samples labelled A, B, C and D and asked to test their pH using pH paper. He observed that the colour of pH paper turned to light green, dark red, light orange and dark blue with samples A, B, C and D respectively. Which sample is most acidic?
\nAnswer:<\/strong><\/span>
\nSample B<\/p>\n
\nA student observed that the colour of pH paper changes to green when she dipped it in water. She added a few drops of concentrated hydrochloric acid to the water. What change in colour she would observe on pH paper?
\nAnswer:<\/strong><\/span>
\nThe colour of pH paper would turn to light red.
\n(Reason: The colour of pH paper is green in neutral medium while it is red in acidic medium).<\/p>\n
\nFour students A, B, C and D measured the pH values of water, lemon juice and sodium bicarbonate solution. What is the correct decreasing order of the pH values?
\nAnswer:<\/strong><\/span>
\nThe correct decreasing order of pH values is lemon juice < water < sodium bicarbonate.<\/p>\n
\nA student test a sample of drinking water and reports its pH as 6 at room temperature, which kind of compound do you think may have been added to water?
\nAnswer:<\/strong><\/span>
\nAcidic compound like bleaching powder.
\nBleaching powder in water liberates chlorine which makes its pH 6 (i.e. the solution becomes acidic).<\/p>\n
\nWhich will be more acidic and why?
\n(i) A solution with pH value of 6.0
\n(ii) A solution with pH value of 5.0
\nAnswer:<\/strong><\/span>
\n[H+<\/sup>] in solution with pH 5.0 = 10-5<\/sup> M
\n[H+<\/sup>] in solution with pH 6.0 = 10-6<\/sup> M
\nAs 10-5<\/sup> > 10-6<\/sup> hence, solution with pH 5 is more acidic.<\/p>\n
\nChoose strong acid and strong base from the following: CH3<\/sub>COOH, NH4<\/sub>OH, KOH, HCI
\nAnswer:<\/strong><\/span>
\nStrong acid\u2014HCI, Strong base\u2014KOH<\/p>\n
\nTwo solutions A and B were found to have pH value of 6 and 8 respectively. What inference can be drawn from this?
\nAnswer:<\/strong><\/span>
\npH value is 6, it means solution A is an acid. pH value is 8, it means solution B is base.<\/p>\n
\nDuring an experiment a student accidently spilled hydrochloric acid on his hand. His teacher applied dilute solution of another chemical substance which relieved him from the burning sensation. What could possibly that dilute solution?
\nAnswer:<\/strong><\/span>
\nThe applied solution could be a basic solution like Mg(OH)2<\/sub>. It reacts with acid to form neutral salt.<\/p>\n
\nReena place one drop of each of hydrochloric acid, sodium hydroxide and lemon juice on a strip of red litmus paper one by one, in which case would you observe change of colour of litmus paper?
\nAnswer:<\/strong><\/span>
\n(NaOH) sodium hydroxide.<\/p>\n