Praxis Middle School: Science (5442) Questions and Answers Latest Version with Certified Solutions

Praxis Middle School: Science (5442) Questions and Answers Latest Version with Certified Solutions What is the purpose of a calibration curve in spectrophotometry? To determine the concentration of an unknown sample by comparing its absorbance to a standard series Why is a blank solution used in colorimetric analysis? To zero the instrument and eliminate background absorbance from solvents or reagents What does a higher absorbance value typically indicate about a solution in UV-Vis spectroscopy? That the solution has a higher concentration of the absorbing substance Why is it important to use distilled water in analytical procedures? To avoid contamination that could interfere with results What is the function of an indicator in a titration? 2 To signal the endpoint of the reaction by changing color Why are burettes preferred over graduated cylinders in titration experiments? Because burettes allow precise delivery of liquid volumes What type of substance is commonly used as a primary standard in titrations? A highly pure, stable compound with a known concentration What information can be gained from a titration curve? The equivalence point and pH changes during a titration Why must glassware be rinsed with the solution it will contain during a titration? To prevent dilution and ensure accurate measurements What is gravimetric analysis used for? To determine the amount of an analyte by measuring mass Why is it important to dry a precipitate before weighing in gravimetric analysis? 3 To remove moisture that could affect mass accuracy What is the role of a reagent in qualitative analysis? To cause a specific reaction that identifies the presence of a substance Why is it necessary to use a control sample in analytical experiments? To provide a baseline for comparison and detect experimental errors What is the difference between accuracy and precision in analytical chemistry? Accuracy refers to how close a measurement is to the true value, while precision refers to the consistency of repeated measurements What is the function of a buffer solution in chemical analysis? To maintain a stable pH during a reaction Why should samples be handled with gloves and clean tools during analysis? To prevent contamination and ensure valid results 4 What does a sharp color change at the endpoint of a titration indicate? That the chemical reaction between the titrant and analyte is complete What is a limiting reagent in the context of quantitative analysis? The substance that is completely consumed and limits the extent of the reaction What does a conductivity meter measure in a chemical solution? The ability of the solution to conduct electricity, often related to ion concentration Why is repeated measurement important in analytical procedures? To increase confidence in the results and identify outliers How can errors in analytical chemistry be minimized? By using calibrated instruments, standardized methods, and proper lab techniques What is meant by the term "standard solution"? A solution of known concentration used in quantitative analysis 5 What is the main goal of analytical chemistry